Of course you don't beat the living daylight out. You are a very concientous horse owner, it is clear.
You know, of all the bad habits of horses, having them try to bite you when you tack up is one I hate the most. I just hate that being on edge , waiting to see if they will bite . It makes one nervous, and of course, the more you are nervous or worrying about something, the more the horse cues into it and lives up to your expectations. I would hate it if I had to deal with that a lot. Dealing with my friend's horse was not fun and I tried to be quick and decisive, but I tend to just be glad that the horses I ride aren't like that.
It might lessen as she finds there is no pain associtated with being girthed up.
One thing you definitely do NOT want to do is to keep your hand up in the "ready " position, just in case. That comes off as a threat and the horse will often be resentful of the pressure that is constant like that.
You can, however, keep your elbow kind of 'cocked", with the point of it sticking out. It isn't pointing AT her, but is off your body such that she will run into it before she runs into your side or shoulder.