Definitly pregnant, id say about 2 weeks before she drops. keep an eye on her after 1 week just incase its earlier.
They will breed every 4-6 weeks, when the male pierces her with his gonopdium (have sex in other words) the female can store sperm packets and have fry for up to 3-6 months from just one mating, even if you take the male out, she will continue to have fry every 4-6 weeks for up to for a few months at least.
This is the same for all livebearer fish although swordtails can be more at the 6 week mark rather than the 4 week.
Also, dont listen to most people about this gravid spot buisness, they are wrong, no desrespect to anyone by the way.
The gravid spot is always there, people just think it gets darker when pregnant but this is not the case, the gravid spot is always the same colour, it just appears darker because of the babies eyes like guppyman said, but its nothing actually to do with the gravid spot.
Even virgin females have got a gravid spot, i have 20 virgins ready to mate with a specific male, and they all got gravid spots, some draker than others, but i can garauntee you there not pregnant.
Hope this help ya