GIRLS? Could a girl get annoyed at this?

Yeah that could be pretty frustrating. If she likes you, she could have been expecting some nice conversation (or even you asking her out, who knows), and in that case it would be even more frustrating. My guess is it hurt her feelings that you initiated a conversation with her, then left her waiting for 10 minutes because you were having "the best convo ever" with someone else. The fact that she likes you, and you were talking to some other girl just makes it even worse. Ask her if she's mad and talk about it.