I agree.She doesn't seem to be favoring it much at all.
I had one once that had a similar swelling which turned out to be pus from an infection that might have entered when she ripped of her toenail. Being the way I am I decided to drain it, which confirmed it was pus, then I started her on antibiotics.
@Matzwd, I am not suggesting you try draining it, especially since you're taking her to a vet!
The main difference between our two birds is mine was dead lame and yours is not.