Mares can be witchy, especially if she is an older, more dominant mare. She probably hasn't had the foundation of groundwork put on her for her to know humans are 100% the boss.
I would definitely go about correcting her asap. I've helped a lot of beginner horse people out and the number one thing they seem to have trouble with is letting their horses get away with things a more knowledgeable horse person wouldn't. As they let the horse get away with something, the horse will try it again and get progressively worse until the beginner can't handle it anymore. You don't want to let that happen to you.
If the mare does anything agressively again, you need to do something to catch her attention in a not so nice way. I don't like using stud chains, etc. I would rather chase after her until she thought the hounds of hell were after her, popping her/driving her away until I decided she has had enough. Catch her and go about your business as if it never happened. It won't take her but a time or two to figure out she wants to play nice.
The worst thing you can do is let a pushy/dominant/onery horse know you are frightened of them and not correct them. Good luck!