Pregnant Fish Eating Plants

[Cocoboy821]

Hey guys! I have a question that might or might not go in this section, but it seems like the best area for it. My husband and I have a 20gal tank with 6 platies living in it. One of our female platys is pregnant for the second time, and has been caught as the reason some of our ferns in the tank are just stalks. None of our fish have nibbled so much on the plants that the leaves disappear. They get fed flakes in the morning and frozen food at night. She's already eaten two bare and I just caught her starting on the third. She didn't do this last time she was pregnant, does anyone know why she would all of a sudden start? She's the only one that we've seen constantly eatin the plants.
Thanks in advance for any thoughts!