What's up with this lady?

There's a lady, about 10 years older than me, who is always finding some way to correct me about something or be rude to me. Even when I say something that requires no response (i.e. An email that says "Please meet our group in front of the building at 12pm), she will respond to everyone in the group with something snappy like "who said 12pm? It makes more sense to meet at 1pm." She'll also see me doing something and come over and tell me how to do it or take over and re-do it as if I wasn't doing a good job. My question is what is the problem? We have no negative history besides her quips.