I NEED HELP!!!WHats wrong with my aqaurium fish??!??!?!?

my pregnant Dalmation molly, cannot swim at all.We've kept her in a breeding tank recently and she didn't push out any babies, when we tried to take her out of the breeding tank she jumped to the other side of it,then we tried to take her out again with the net and we got her and put her with the rest of the fish in the tank. She seemed to be fine after wards,she was swimming all around the tank and one of our male fishes even started to sniff her butt. But this morning now i didn't see her in the tank. But then I noticed that one of my other female fish was picking at something behind our aquarium skull.It was the pregnant fish that i was looking for,she couldn't move, she wasn't completely upside down but she was slanted, it seems as if her tail is broken,she cant move it at all.we tried to like push her down the correct way with the net but she just floats right back up.she is still breathing at the moment but she didn't eat(evident ally because she cant get up straight) but shes still moving her fins and opening and closing her mouth. She is now back in the breeding tank away from other fish and we put some stress coat in there.But if she really were pregnant, shouldn't she be laying down because she has more weight because of the the babies??But i really have no clue what to do at this moment someone please help.