I started to read all the replies until it started to go down hill on generalizations about various disciplines.
My take on your situation is, as long as you’re keeping your horse engaged as you are in groundwork I don’t see what can be gained by rushing it. I think your timeline is spot on. Sure some TBs need some down time before they are restarted, but if yours is showing signs that’s she’s ready for some work, by all means do it. You can do plenty without riding her. That doesn’t mean. you can’t get a lot done.
Once you get the basic groundwork established, look into in hand work. There’s a book called “Right From the Start” that shows how you can literally mimic under saddle work from the ground. Unfortunately it’s out of print and hard to find. In a nutshell, you work with the horse in a bridle. You stand at her left side near his shoulder (trying to mimic where you would be if you were in the saddle). You hold the reins as if you were mounted. Just as if you were riding, your shoulders mimic hers and your legs move her hind end. You reach over to the right rein to not cross it over his neck. With the taller horses, you get tired quickly since you’re holding your arms up, but it’s amazing what you can accomplish. It’s a safe and pressure free way for the horse to get used to contact. Initially they stand there like “what are you doing”, but once they get it, you can walk them around, do half halts, leg yields, turn on forehand, etc. You can teach contact and build top line without ever sitting on her.
Stay your course and trust your gut.