It certainly looks gravid ( pregnant ). I would say it's likely to give birth soon. I have found with most live-bearers that a sure sign a female is soon to give birth is that the males start paying more attention to that female. If you have a breeding tank ready I would move her but try to match the temperature and chemistry as best you can first so as to minimize stress. Assuming your breeding tank is smaller than your main tank I would fill the breeding tank with water from the main tank and put new water in the main tank, that way the chemistry should be the same.