It's wrong. I'll look at it from both moral or health perspectives. At 8 months she's already in her third trimester and near labour. She's heavily pregnant and would soon deliver.
As such, everything that could serve as a risk factor towards developing any complication or complications to the pregnancy should be avoided, including sex.
Having sex at this point does not directly translate to automatic complication but could put the woman in a possible state of having one. So it's better to avoid completely at this stage.
Morally, the first sex that led to the pregnancy is wrong, it's fornication. She wasn't married. Having sex now with another man in the absence of baby daddy to be is still wrong, it's still fornication. It will only worsen things for her, it may lead to pain and more hurt.
At this point, she just has to find a way to put her body under subjection until safe delivery of the child. After that, let her get married to someone else if she chooses so and enjoy her communal rights in totality.
If she is single, then she can do whatever she wants.. But if she has some religious beliefs that is against pre marital sex, then it is best to abstain..
Of course, it is morally wrong.
Honestly, I don't like the sound of it. And it's worse if it's my baby.
But then, she isn't in any exclusive relationship. It's her body and so the choice belongs to her