If she has terminated due to a certain gender I would say she must have a genetic reason to choose this. Some conditions only affect a certain gender. Can't list what they are as I don't know most of them. Haemophilia is one (it can affect girl but is very rare) but not sure what some of the others are.

It is very rare to be only able to carry one gender although it does happen. Alot of people self diagnose or assume they can only carry one gender however most of them its probably more of a terrible co-incidence to m/c or have stillborn babies of a certain gender. Medically it is rare.