There's no point in rushing something that will eventually happen
I broke my QH mare when she was 2, but I only hopped on her for a few minutes just working on walking & turning. We probably rode once a week if that (for like 15mins). My mare's knees didn't fully harden until the next year around late spring/summer ish - so I couldn't
ride her often without potentially hurting her growth.
I'd say just keep having the trainer come out every once in awhile to get the basics down & let her have a nice winter off. She's got time when she's three or four. Heck my trainer doesn't even start her WBs until they're like 5.