At this young an age, it's not about discipline. It's about REDIRECTION and REPETITION. She may understand what the pop to her hand is for at the time, but she's not mature enough to remember it, to make sense of it, so that she can learn from it and remember not to pinch in the future. You still want to address her behavior but just don't expect it to stop. After months, and I mean months, of doing the repeatition part ("hands are for hugging and playing, not hitting", "gentle touches only", etc.) one day they just start to get it. But they have to reach that maturity level first and that won't happen for a while. What worked really good for us was to take his little hands and rub them very softly against our face and say "gentle". This teaches what gentle actually means. As he got older, we expanded to "gentle touches". Now that he's over two, we can actually tell him "pinching means time out!" and he gets it.
Redirection is when you put her down, and get her attention on something else. She's not pinching you to be a brat, it's how she explores her world and your world and both of your emotions. It's an excellent opportunity to SHOW her what you expect of her. Say "Ouch, mommy hurt" (or something like that and take her hand and show her gentle, put her down, and give her a toy.
Here's a link to a question from another mom on here who has questions about discipline. Even though her child was older than yours, you may still be able to use some of the advice she got.
http://www.mamasource.com/request/15975027431807385601
Dr. Sears is the bomb! You gotta check out this link to his article on discipline.
http://askdrsears.com/html/6/T060100.asp
There's about a whole day's worth of reading in this one link, but there's some good stuff here!
EDITED TO ADD:
I just read some of the other moms responses and feel the need point out that out of all the mommy boards I've ever visited, Mamasource has the "harshest loving" moms. You've gotta do what you feel is right, A., with your own baby girl, but I can tell you that most of the moms I know (either online or in real life) do no bite or hit or pinch their kids back as a way of discipline. Teaching a baby/child to not cause pain by actually causing them pain boggles my mind. And come on people, A. has a 9.5 month old here! We're not talking about a toddler. Geesh!