Your platy is not that far on if you take away that over fed belly, your feeding her a little to much, lay off the feeding for a few days, just feed twice a day, small amounts, morning and then night, she will return the natural size she should be without the dropped down belly at the front.
have a look at this pic i have done (more info can be found in the link in my signature.)
"Your fish is the red line"
Black line - Her normal size how she should be.
Red line - Over fed (belly dropped too much at front)...
White line - How she will look when heavy pregnant.