Dealing with annoying co-workers

This topic does not involve swimming AT all ... sorry ... I cannot stand my co-worker! She drives me crazy. First of all, I work in a very small law firm. There a total of eight employees. Four attorneys (one is part time), two secretaries, an errand boy (aka the head partner’s son), and myself. We have an open office sans cubicles. So there is NO escape. Moving on ... we are a very busy firm. Normally we have a couple of law clerks but right now we don’t. So most of the extra work falls on me. We don’t really have carved out jobs really we all kind of do everything. Though we do all have things that only we do. The annoying co-worker complains non-stop all day long. Seriously. Either she doesn’t have enough to do or the guys ask her to do stuff and she flips out “I don’t have time for this. I can’t handle this right now.” She complains about everything she is asked to do. She complains and/or comments on every phone call she answers. She gets all snippy with me and has basically told me that if I keep eating the way I do (I snack on healthy things all day) that I am going to get fat, so I should enjoy it while I can get away with it. She talks endlessly about how her son is in marching band and how that is the most important thing EVER, how hard it is and how much time it takes up ... I want to yell, do you know how many hours a week I spent in a gym in high school? Like, 30! AH! I can’t take it. I seriously want to yell SHUT UP! Everyone is busy and no one cares. She is a drama queen to the max. She is ALWAYS in pain, her knee, her back, she has a headache, a stomach ache, a cold ... she hasn’t been here everyday all day for two weeks since I started in September. It drives me crazy. I am really afraid that one day I’ll just blurt out shut up you whiney wench! Gr! Do any of you have annoying co-workers and how do you deal with it? Thanks! Usually, I am not a complainer I swear, and I do see the irony of complaining about someone complaining.