You got to keep a reiners mind busy. I would do arena work and if she is a finished reiner then do less arena work just do touch ups, I would spend most of the time doing hill work building muscles back up.
My two reiners do this.
They walk 2 miles a day and thats including 2 hills when im getting them in shape. I will spend a week before a show in the arena just doing some touch ups but not drilling. Like you do walking, trotting, loping. I work on transitions from going to the fast lope to the slower collected lope.
I have a 5 year old almost finished reiner and a 14 year old finished reiner. And thats what I have done with them for 3 years and its worked great. Reining like any horse sport is tough on the legs so I try to save them as much as possible :)
Congrats on your purchase thats great!!!!! Happy for you and bestest of luck with everything that you do!!! Make sure to keep us informed