Isn't a key point that this is complex and without knowing the full context or about the friend and her attitudes towards relationships and sex it is very hard to say.
It is possible that this could be a good or neutral idea for her. In her late pregnancy she MIGHT be feeling confident and positive about becoming a parent, happy to be rid of last partner and secure in her single status, and MIGHT just be feeling that she wants uncomplicated sex and can have that and walk away with zero impact on her or the baby. She MIGHT have known this other person for many years and think he is likely to be around for a good while and that she wants to get started on this relationship now and and it will deliver good outcome so or her and the baby.
Or it MIGHT not be a good idea for her because she knows that she is unlikely to be able to have sex with this man and walk away with zero impact on herself and that impact might last to the time she gives birth and beyond. It MIGHT be that she is concerned about how this will impact herself emotionally (with knock on effects to the baby in pregnancy and beyond) or that this man will then be around when the baby is born and MIGHT be unsure if that will be a good thing for the baby.
We don't know.
I would say that although Jacques rightly says that not all women feel vulnerable in pregnancy and that some women will want to and be able to have strings -free sex, that actually turns out to be as simple as they hoped, these women are in the minority. For that reason, and because this is a scenario where we don't know the woman and her circumstances, I think any advice given has to be on the cautious side.
This is a woman who is fairly heavily pregnant and who has undergone a significant relationship change in the last few weeks. She was having a baby with the baby's father and now she's doing it alone. However much she wanted that break-up (and we don't know about that) she still finds herself in a situation which probably wasn't what she envisaged. That in itself puts her in a complex situation. She has had to adjust to the idea of parenting alone. She might be entirely happy with that or it might be that she's had to become resigned to it. It wouldn't be surprising if she was emotionally fragile a few weeks after a break up and before having a baby for the first time. She may wellness age the instinct many women have to protect themselves, to aim for stability and to protect herself and the baby. Remember the foetus is affected by what happens to the woman and things like relationship break downs which have already happened impact act on the growth of the foetus. Having undergone a significant event already in this pregnancy she is right to at least be cautious when contemplating this new man. Those who say she should just have sex if she feels like sex, without suggesting first that she cautiously consider it, precisely because of her context sound irresponsible to me. Context is very important for all of us. She will have an idea if if this will just be casual and also of whether she will actually have control of that. Some people claim they can always keep sex casual with zero emotional impact on themselves, but others have hoped for that and found it out of their control and more complicated than when they first embarked on it. It might well be, that being oregnant makes it more difficult to know exactly how you will feel and respond to a situation. Lots of oregnant women are surprised at how they react and feel. It could be that this is likely to become a bit more than just one off sex and friend might be considering if she wants this man around when the baby is born.
Some people have been really unpleasant on this thread. Most have thought it was a bad idea even if they haven't been unpleasant and even if if other circumstances of not being oregnant they would simply say 'go ahead'. I do think being pregnant is a factor here. People urge caution not because they think a single woman shouldn't have sex or a pregnant woman shouldn't have sex or start a new relationship, but because they can see that this woman could very well be vulnerable and the so-called strings free, zero impact on mother or baby sex, could well turn out to have impacts, even if theyvar not intended or wanted. Inthinknits this which makes people urge caution or avoidance but they don't always express it well.
In this situation the friend is unsure. She is seeking advice from OP and it's good that she is carefully considering it. If in any kind of doubt at all, I'd simply say, listen to that doubt and don't do it. She may have an urge for sex but should listen too. O what her instinct so bout whether It's a good idea are telling her. Her life has been complicated enough recently. Unless she can 100% guarantee (and I'm not sure that's possible) that this sex can happen without any impact at all on herself, then for her own self preservation at this time, it's just best avoided.