It is so hard to tell from pictures. But if her belly continues to expand, you can be fairly certain she's pregnant. Four weeks or so from time of conception, but it's quite hard to know when fry are due if you don't know when she got lucky.
Provide floating plant cover, so fry have a place to hide and some will survive, especially if you make sure the parent is well fed.
Live or frozen foods are very good for pregnant fish and for fry too. They provide some animal sourced fats the fish really need when young, and for developing young. It's not a disaster if you can't do this, it is simply better if you can. Like anything else, fish are what they eat.
