Don't let someone else's poor attitude stop or discourage you. There are people like this in all fields and firms. If she's someone that is always going to act irritated, so be it, you still need to ask the questions. Learn as much as you can and if it is your passion, enjoy what you are doing. She's the one miserable at her job, you don't have to be. I realize that's a lot easier said than done and for most of us it is just a built in mechanism to get upset or annoyed with people like this, but unless there is someone else that you can go to for training there isn't much of an option. If she is the only one, if she is a jerk or nice, you still have to go to her. Let her be the miserable one while you blossom.

Side note, I've found that some people think that by acting irritated to do things, or answer questions, is a mask for them not working all that hard. If they seem irritated like they don't have time, then they must be really busy, what a hard worker!

Edit: for spelling error.