Advisor walked in while I was complaining about her; How can I minimize the damage to our relationship?
From what you have said, I am not sure even if she heard you. All you need to do for now is to STOP this attitude. You will never find a perfect supervisor... Yes, you can talk with a friend about how difficult your life is with this supervisor. But this should be out of the lab and avoid -- as much as you can -- other students with the same supervisor. 


Show her that you value her research and expertise (in case you don't value her research, then find another supervisor).
Do not talk about anything happened unless she started the talk.


I completely disagree with @Penguin_Knight on the gift thing. Being so nice in a typical meeting indicates something weird is happening. Do not do it. (I believe this is a cultural thing some people may see it really good others will think about it in a very bad context.)