Well, given the fact that it's almost certainly her husband's kid after all, I can understand why she wouldn't want to abort "just in case".
If this isn't a scam, maybe she needs counselling? She is over-reacting to a rather small risk.
It's possible to get a home DNA testing kit which would avoid the legality problem of testing an anonymous/non-consenting father, but fuck knows how she'd get a sample of the kid's DNA before birth, in that situation. Would a clinic take a sample, knowing that she would then use it in an illegal test? They might, that might not be illegal in itself, if they aren't the ones doing the testing.
If so, then maybe she can get some of her husband's DNA wthout his knowledge, no need to involve the punter at all.