Tokis-Phoenix
^_^
well if you have a quorntine tank you could move the prego one into that and once it has its babys you could put it back into the other tank to make sure all the babys live. she will also be pretty weak after birth so your fish might be pickin on her. i kept 5 of my mollys because out of two prego ones those were the only ones that survived. if you don't want to keep all the fry i beat an lfs would take them off your hands for store credit.
The only problem with this though is the majority of lfs will not take fry in, only adult fish, as fry are so sensitive and often end up dying.
This means you will have to raise the fry for at least 6months until they are getting near a decent size before any lfs will take them off you, this of course though is a problem if you don't have enough space to raise them in properly the first place. You will need to speak to your lfs will take fish in at all though first of course.