It's hard to tell. I only really know, just before she will give birth that day when her stomach will look boxy, squared off. Sometimes I've seen the outline of one of the fry, looks like a tiny ball shape protruding through the skin, usually very shortly after that mayb as soon as an hour she would give birth.
If not this week, I'd say next week she will pop
If not this week, I'd say next week she will pop