Is there anything that it could have caught it's neck on? A small bit of wire sticking out of a cage, anything like that?
I think you should just monitor it's size for now. If it starts to get bigger then you may want to drain it. It shouldn't bleed very much if at all. You would require a...
Has she had any injections at all on that side? I have seen swellings like that around an injection site.
I have also seen the same thing on a wild bird after having a puncture wound from a cat.