all females have gravid spots but if she is fat then she probably is pregant, it is almost impossible to tell on other peoples fish but normally a picture helps give a rough estimate, also look out for her stomach area going sort of square shape, if she does this she is close to givign brith
As she very large then she's in the later stages of pregnancy so I'll say with in the next 10 days as a stab in the dark, but if stressed or shocked she can hold them even longer, or in worst cases abort them.