hiya, depending on how ready to pop she is i wud leave her in the main tank if she is that close, as it cud stress her out and she will terminate the pregnancy. but if u think at least a week to go, then move her.
the main thing i wud advice if u can, is to get sum floating weed, that way if u leave her in the main tank, the fry will swim into the weed and be safe for a lil while. this is what i do, as i dnt like moving pregnant fish. but what i find is the most effective way to save the fry, is to move them into the small tank where they can be alone, or put them in breeding nets. i usually try and stay in doors around the time their due to give birth, that way i can move them faster, and save them b4 the other fish eat them!
hope this helps u, gud luck!!!