Normal gestation period is 25-28 days. Are you sure she's pregnant?
Not for mollies they are more like 45 days. I hear your first drop takes longer and they can hold fry for a while, they do not necessarily kill the fry this way. My guppy female held fry for almost 2 1/2 months before birthing and my molly female has been pregnant around 70 days and still waiting for the fry to come. Is she being housed with a male? The male could be harassing her by trying to mate constantly and that could stress her into holding or miscarraige.
Offer her more hiding spots, maybe a little salt if your other fish can tolerate it and remove her from any males or even females if they are nipping and be patient. She could be totally fine and just taking her time on the first drop with you.
My female guppy was in a 40 gallon with 2 cory cats for around 6-8 weeks before she dropped, my molly has been with the guppy and corys for over 4 weeks (after spending a few with a male) and still has not dropped.
Just to touch on the other comment, gravid does mean "heavy with eggs" so the gravid spot is more an indicator of eggs than fry, with mollies you may actually see fry's eyes inside her belly when she is about to go and females do plump a little when gravid. However if she shared a tank with a male, she is pregnant most likely.