the mother could have dumped her fry already and this is the last one left. baby fish usually end up being a snack. i believe live bearers are also capable of releasing one or two fry at a time over a period of time rather then all at once. ive def. had them drop alot at once though, so this may not be the case.
getting fake low grassy plants or live java moss is a good idea for the fry too, but a breeding net or tank will increase success rates.
whenever i keep these kinds of fish though i let nature run its course, the fry make a good source of natural food and the ones that do survive to adult hood usually are the smartest, healthest, and strongest out of the group, as to why they survived.
ofcourse thats only my two cents and we all know how much thats worth these days...
what size tank is this and what else is in with them? i feel as if the other fish got to them first.
anyways, welcome to the forum.