Wow!!! She looks great!
If it's a smaller open show, you could probably get away with a long mane or you could band the mane. There was a 2yo pleasure horse being shown a year or two ago that had a long banded mane, it looked pretty. I show my rope horses, with long manes, at open shows in the halter and riding classes.
If you are going to a breed show, you should probably pull it. I feel your pain, I never thought I'd say this, but since I've had the rope horses, I really prefer the long manes.