Hi,
You can't rush these things. She'll have them when she is good an ready.
My female platy has loooked huge for 2 weeks and yesterday she started sitting on the bottom,hiding and generally being tetchy. I thought tomorrow i'll set up the fry tank and put her in it. This morning I check on her and think that she seems smaller and she has only gone and had them behind my back. I found 1 fry alive and who knows there maybe more but with my 2nd platy who is fat but not huge I am taking no chances, as soon as she looks huge she is going to be put in.
Hopefully she'll give birth soon and probably when your not looking.