How big is she? While that sounds like a good workout, I agree with others that if you've built up to it gradually & she's coping fine, chances are, she's... coping fine! Fitness/exhaustion-wise anyway.
I agree with Kayty about soft tissue & considering her previous lifestyle tho, particularly with a heavy-ish rider. It's not just soft tissue though, but bones & joints too. As astronauts have found in space, if you don't use it, you lose it - bone density & therefore strength will need to be considered in the work you ask of her, for quite a number of months at least, not just weeks. Aerobic but not high impact exercise will be good for her. I wouldn't personally be doing any cantering or other high impact work with her for a while yet.
A few thoughts on your feeding...
we feed her alfalfa twice a day. she also gets oatmo every day for the calories to fatten her up. and it has done a great job of that. she is now at a pretty good weight.
What else does she get? Pasture or hay? If not, I'd definitely be adding that, along with a good nutritional supp that fits her diet. Lucerne/alfalfa is a great high energy feed for horses generally, but it's very high in protein, calcium & other nutrients so it's important to feed it as *part of a balanced diet*. Feedxl.com is one great resource for sorting out that confusing subject.
So far as can see, 'oatmo' is just oaten chaff with molasses added. If that's the case, I wouldn't be feeding it at all. High starch/sugar diets are not good for horses. Bit like living on junk food. If you need to feed chaff, to mix nutritional supplements or other hard feeds with, you could use straight unsweetened chaff, or alternately soy hulls or beet pulp or such, which are also high energy feeds for weight gain but low in sugars.
so i began giving her crimped oats. started slowly, about 2 cups a day for a few and then began to increase it to where now she gets 32 oz. of these oats daily. But only on the days she works.
Why are you feeding oats? If the horse is a good weight now, why give extra energy? And while oats are more easily digested than other cereal grains, they're still high starch & not the best generally. While you're not feeding a huge amount, horses need to be fed little & often, particularly of starchy type feeds, in order to get much from it, but more importantly, to minimise common problems which come about from feeding a sugary/starchy diet. If you're going to continue feeding them, I'd make it a bare minimum of 3 small meals daily, not just on the days she's worked.