SpdDrv, my hat is off to you for devoting yourself to this baby. From what you described, she is very attached to you and very responsive too.
You mentioned she is in a stall. Does she also have a safe contained area where she can run and exercise as well as the stall? The toys are a great idea to introduce her to different objects and entertain her a bit, especially with widdle teeth erupting. Btw, if she seems out of sorts or cranky sometimes, that could be why.
An idea for her stall might be to have a radio on a soft music station which might help your little orphan. Lots and lots of bedding she can snuggle up in since she doesn't have mama to curl up with.
The more touch you give, the better, and it sounds like the two of you are bonded :) With her trust in you, any training will come almost effortlessly as she knows you won't harm her in any way, and it sounds like the two of you are going to be quite the pair, and she will learn quickly when you offer her a new learning experience.
Here is a not too well known training tip: horses have two hemispheres just as we do, but they can't cross-reference concepts like we do, hence they need to be shown a new thing on both sides of the body to fully comprehend. Depending on what you're showing her at any given time, something to keep in the back of your head.
Another very important concept, especially with an orphan, is to provide body contact if/when she is nervous or frightened, and in general babies love and need tons of body contact anyway like all babies do. Horses in general instinctively seek out another horse and make bodily contact when frightened, and you'll see how they comfort one another in their own language by one horse draping his/her neck over the other's neck or back area.
(I do the opposite of what most owners do when a horse is scared - I bring them in to me, or let them enter my space for comfort, not push them away, and addressing their needs in their own language builds incredible trust. There are times of course when that isn't appropriate, it's a matter of knowing when it is and isn't.)
She may do things which are appropriate for a horse but not for you lol, so if for instance she rears up and wants to be playful, please be careful about reprimanding her but be safe too. I had a orphan POA colt, for instance, who snuck up behind me and suddenly I had a hoof on either side of the front of my shoulders, and I turned around and said "Andy, NO!" and laughed so hard I almost fell. So get some knee pads and a helmet ROFL. He never did it again, and no I wasn't hurt, and yes he is a happy, well-adjusted and beautifully mannered little guy. But he was an orphan, and orphans can do off the wall things without realizing what they're doing isn't normal.
I'm going to surf the web and see if I can find a couple of videos I think you might find helpful about body language.
The younger they are, I think the sooner you can show them how to give their feet to you, without using anything - no halter, lead rope, nothing - the better off you'll be. And like you're already doing, keeping the lessons brief. One thing I learned is how important it is to make huge fusses over them as a reward. I make a big to-do about them, and there is nothing like that look in their eyes that just beams with pride and confidence in themselves!
My thoughts about her diet: at what I'm presuming is her age about now, 8 weeks?, you might try mixing some mare & foal feed or some senior feed in with the milk pellets, and soak that into a mash using some of the milk mixed with a little water. She should be nibbling on hay, I hope so, and if you give her free choice grass hay and a little bit of alfalfa but not too much - too much protein is as detrimental as not enough - with a salt/trace mineral block, and if she is able to get plenty of exercise, you likely won't need to supplement her with anything else. I think probiotics are a good idea, I would ask a vet you trust what he would recommend for her, these are just my own thoughts and opinions.
It doesn't sound like there are any suitable horse mentors available at your place right now, and when she's older and it comes time to introduce her it I would suggest being careful. She will probably be both terrified and exhilirated to see another horse, and will probably need time from a safe pen or pasture to just soak up horsie lingo from a distance and get caught up. That'll save you a potential vet bill too.