Molly floating Randomly?

My female molly is around 6 to 7 months old, she has been really healthy, only had ick once or so. Any way i have 2 female mollys(sisters/same age) and the father and a male guppy. The father and male guppy have been chaseing just the one female molly. When she stops swimming she floats vertically. My friend thinks she is acting like that so the males will stop follwering her but im worried. Is there anything i can do for her. Ive already lost the 3 fry of that litter i dont want to lose another one.