In a live chat, Prudie advises the sister of an underage girl making sex tapes with her boyfriend.

Emily Yoffe, aka Dear Prudence, is on Washingtonpost.com weekly to chat live with readers. An edited transcript of this week’s chat is below. (Sign up here to get Dear Prudence delivered to your inbox each week. Read Prudie’s Slate columns here. Send questions to Prudence at prudence@slate.com.)

Emily Yoffe: Good afternoon. Let's get to it.

Q. Sister's Underage Sex Tapes: My little sister Rebecca recently confessed to me that she and her boyfriend Tyler have been filming themselves having sex. She says it excites her, because she's always felt pressure to be a good girl. Our parents aren't rigidly conservative by any means, but I know they'd object to Rebecca making sex tapes, not least of all because she's 16 and Tyler is 19. I'm not sure what to do, because I am worried my parents will lose their heads if I tell them. But, as I pointed out, Rebecca is underage, and it won't end well for Tyler if the authorities are alerted. As an older sister, what's my duty?

A: I hope most teenagers don't think that the alternative to being a good girl is being Paris Hilton. Your sister confessed to you for a reason, and it's good that you were apparently so flummoxed by what she said that you didn't offer much of a reaction one way or another. I think 16-year-olds should hang onto their virginity. I'm sure there's a study somewhere saying that keeping horniness in check correlates with higher trigonometry scores. But now that you know your sister is sexually active, the first thing you should do is to make sure she is using birth control and that's she's seen a gynecologist. Tell Rebecca you'd like to enlist your mother in this, and that you will not mention anything about her cinematic ventures. As for the tapes, I feel kind of sorry for today's youth, whose formal sex education consists of lectures on lethal illness and the potential for being prosecuted. But I agree that underage sex tapes are a bad idea, both legally and morally. Tell your sister you're really glad she came to you, you've been thinking about she told you, and it sounds as if she feels she's gotten in over her head. Explain it's not too late for her to change her mind about her extracurriculars. No, she can't get her virginity back, but she can decide that concentrating on getting through high school, instead of exploring her sexuality, is a better focus. Be calm and nonjudgmental. Then when the conversation progresses, you can suggest she get all copies of the tapes and destroy them.

Dear Prudence: Worst Grandparent Visit Ever!

Q. Regretting My Past Actions: A couple of years ago my then-boyfriend broke up with me because I was too clingy and unstable. I couldn't see it then, but in retrospect I totally agree with his diagnosis. I was convinced that if I tried hard enough he would love me again. I spent many months calling him at home, at work, even his parents' house, to the point where he changed his numbers twice. I always found out his new numbers and texted him repeatedly to beg him to reconsider. He felt sorry for me at first but he quickly became hostile (understandably) as I turned more desperate. I heard that he even considered getting a restraining order on me. I really made his life hell. To cut the long story short, I started receiving therapy and did a lot of soul searching before realizing what a messed up person I was. I couldn't see it before but now I feel completely ashamed of my behavior. I want to send a final letter of apology to my ex—not a phone call in case he finds it too confrontational—and tell him how sorry I am to have harassed him the way I did. However, there is a part of me that thinks he probably never wants to hear from me again and it's best to leave him alone. What do you think?

A: How wonderful to hear that you sought help, it worked, you can now you can see your behavior from a different perspective, and that you are committed to making permanent changes. You should discuss with your therapist your desire to contact you ex about how much you've changed. He or she can help you examine this impulse and see it from your former boyfriend's perspective. I think you're right that he never wants to hear from you again. A letter saying, "Guess what, I realized that I made your life hell, so I'm writing to let you know I'm sorry and after this letter I will continue to leave you alone. Unless you write back a letter of acknowledgement, in which case I'll respond …" is bound to go over badly. The best way you can make amends and continue to heal is to leave your ex alone and move forward.

Q. Family?: My husband's youngest sister and her husband are infertile and had several rounds of IVF with no success. They approached me and my husband about surrogacy. I reluctantly agreed, after a lot of pressure from my husband and his family, and was implanted with embryos consisting of my sister-in-law's eggs and donor sperm. I am now six months pregnant. Last week we found out that my sister-in-law left her husband and is now living in another country with a lover. Brother-in-law told my husband last night that he was filing for divorce and wants nothing more to do with our family, including this child I'm carrying. We are attempting to contact my husband's sister but she is not returning our calls. We know she is OK because she has been in contact with his parents and has "explained the whole thing to them." We, apparently, are not going to hear the whole story and I have no idea what is going to happen with this baby I am carrying. My husband said we may have to keep it and raise until his sister figures out what she wants to do. His family agrees. I feel like I have fallen through the looking glass. Our youngest is 7 years old and I do not want to have to go back to diapers, bottles, and midnight wake-ups. I also don't want to bring a child into our home and raise it never knowing when his sister might show up and take it. No one is listening to me. I don't even know what legal obligations I am going to have toward this child. I can't even think straight right now. I would really appreciate some advice.

A: You need to do what you should have done before you got near a Petri dish: Contact a lawyer. Yes, it's a little late, now that the baby is gestating and both parents have taken off, but you need an expert in surrogacy and family law to help guide you through this mess. The parents who enlisted you surely have some legal obligation to you and to the fetus you're carrying. All this, including the option of placing the baby for adoption if no one in the family wants to raise this child, has to be sorted out. You can't do this alone; get the law on your side.

Q. Neighbor Keeping Another Family's Lost Dog: My neighbor recently adopted a dog with distinctive brown and black markings. Last week my daughter brought home a LOST DOG flyer with a picture of a dog with the exact same distinctive markings. The flyer detailed how much the owners missed their dog. I brought the flyer to my neighbor's attention and told her I believed the dog on the flyer was the dog she adopted. My neighbor curtly told me to mind my own business and snatched the flyer from my hands. Now I'm not sure what to do. I'm 99 percent certain my neighbor's dog is the lost dog. Should I risk being wrong and ruining my relationship with my neighbor?