What Hummer Is This?

This little female hummingbird has been irregularly showing up at our feeder for the past month, but I just finally managed to get some pics...and she confuses me. 

Am interested to hear people's guesses as to ID and why they think so.  I will save my own thoughts so as not to bias others, but I did observe that the few times she has perched near the Anna's regulars (a male and female), she was smaller than either.  Today she and the female Anna's spent ~4 minutes doing a head-weaving display at each other.  Then a little later the male Anna's displayed his gorget prominently to her before chasing her away.