A friend of mine had mrsa on her lip several months ago and was treated with antibiotics. i accidentally drank from her glass recently. should i worry?

Little or no risk: For every person who has had a documented MRSA infection or is known to be carrying it, there are 10 or 20 others that you don't know about. This particular event is no higher risk than all the times to shake hands, socially kiss, or visit the homes of other entirely healthy people. Just use common sense hygiene but otherwise I wouldn't worry about it.