I have owned many budgies and just because a female may be slightly bigger than a male doesn't always mean she may be pregnate. It could be possible but also consider on how much you feed her. She may be just gaining some weight. If you are very conserendni suggest you buy some nest building materials from you local pet store and see if she attempts to build a nest. If she does it may mean that she is pregnate. But sometimes they build nest and don't lay eggs. You could also take her to the vet and get her tested for pregnancy. Hope everything helps.

I'm no bloody expert but birds lay eggs as far as I'm aware so she couldn't be pregnant

The bird on top is a female and she looks fatter than the blue male...does that mean she's pregnant(or has an egg)? Plsss help