If you are struggling to deal with her, I'd go down the "sorry?" route.
It's very nice to imagine that we'll be able to snap back with a witty retort, but in reality, if that's not your style, you won't be able to think that fast. When someone is so rude to you it's hard not to freeze in shock (then kick yourself later).
When you see her coming, remind yourself "sorry, sorry, sorry..." then when she says something catty, you'll be ready. It's the same reply, every time, and it forces her to repeat what she's just said. She won't want to; she;ll seem SO rude saying something rude twice. So she'll just wither and say "oh, nothing" and walk off.
Or if she seems to be in a snippy mood, ask her straight away, "is everything ok?" (obvs you don't really care, but it shows her that you've noticed she's being weird and rude. It will snap her out of it)
Good luck, these kinds of people can complely ruin workplaces. x