How do I slow down my horse's trot?

I got a new thoroughbred filly the other day. She had equestrian training and was a 7 time champ at Churchill Downs. Although, they are looking for a million dollar (triple crown) horse. So they go through them quick and wanted to sell her. She rides well western and I'm going to show her in western pleasure. She was bred to run, so obviously, her trot is to quick for western pleasure. She turns well off of legs, has a light mouth, and neck reigns. So I'm trying to slow her trot down, because I'm a minor and I'll only be showing her in the walk jog classes. So I just need some tips on slowing her to a pleasure trot.