You should weigh them on a small scale, like a jewellers scale, to get their weight in ounces. It's really the only way to know if she's overweight.
Some gliders are naturally bigger, some are smaller. Perhaps the boy is more active on the wheel and playing, whereas she's more laid back and prefers to snack instead?
What are you feeding them? And how much?
You could try adding some foraging toys, or putting parts of their dinner in hanging glider kitchens. That way she will have to work for her dinner. You could also separate the food into mutiple dishes, putting fruit and veg in one, then the staple in another on the side of the cage. If she's moving from dish to dish, she won't be able to gorge as easily.
You might also want to add another wheel, or look into the custom choice cruiser. The full bounce option provides more of a workout.
When I needed my glider to lose weight, I added an extra wheel, removed the hammocks and traded them for fleece vines and ropes for them to climb instead, and added hanging kitchens and put their veggies in the foraging cups (attached to hanging toys).
You could also take her into the tent to give her more space to run around.
But before all, make sure she's actually overweight! If you have a naturally small male, she could look bigger in comparison, even if she's within a healthy weight range. If you don't have access to a scale, a vet could definitely weigh her for you :)