Thank you all for your responses. I can definitely throw a half bale in with her, and we have plenty of half barrels laying around. The baby would end up sleeping on it and smooshing it into the dirt if I don't put it in something.
I'll start by giving her a couple handfulls. Of beet pulp mixed in with her feed and adding salt to the water to hopefully make it more appealing to her.
The tricky part is I don't live on the property and I pay my teenage neice to feed Sky twice a day. If Sky doesn't touch the beet pulp and then it spoils in the heat, how dangerous is that if her or the baby then decide to eat it? That's my biggest worry at the moment.
Again, Sky can not have alfalfa due to her photosensativity. The mare and foal has rice bran in it, so should she be getting more of just rice bran?
Over the years, I've learned that simple works best for me. Most feeds are designed to meet the horses nutritional needs based on the amount fed. Feeding extra ingredients has not worked real well for me, so I try to keep things super simple.
So, my advice is,
Feed the Mare and Foal Feed per instructions
Free Feed grass hay
Make sure they have lots and lots of fresh water.
If you add Beet Pulp, start with a small handful soaked, and put it in with the Mare & Foal, so she can get used to it. I feed about 1/2 lb (dry) to each horse morning and night. I set up their buckets with the 1/2 lb of beet pulp and 1 oz of salt, then I add 2X the amount of water and let it all soak til the next meal. It will swell up to about 2 or 3 times the size of the dry stuff and the pellets will fall apart into shreds. Pellets are generally cheaper to feed than the shreds but take longer to soak. I can buy a 40 lb bag of pellets for 11.99 and the 25 lb bag of shreds is 13.99
I don't use rice bran at all, I found it very expensive and not all that effective. What has worked for me is making sure I weigh the amounts I'm serving to make sure if they should get 6 lbs, they GET 6 lbs at a feeding. Once you have your mare used to getting 6 lbs at a feeding, then if you want her to gain a little faster, I'd just add an extra pound per serving (so in effect feeding for a 1200 lb horse rather than an 1000 horse) until she's not looking skinny anymore and then you can take away the extra couple of pounds of feed.
I feed beet pulp more to make sure they are getting their salt and some extra water during hot or really cold spells. If they are thirsty they'll drink and if they drink sufficiently they'll also eat. I don't know why but a dehydrated horse also seems to go off their feed. For me, beet pulp is the cheapest and easiest way to insure they get thirsty and they like it once they're used to it.
As for spoilage, if it smells sour I don't serve it, it's a sign to me that it's been sitting too long. If you start with just a little bit and mix it in with her Mare and Foal, she should eat it right up and not ignore it, so it won't spoil. When I'm serving up their breakfast buckets I just toss the Mare and Foal or Strategy or whatever I'm feeding, right on top of the soaked beet pulp and I don't even have to mix anymore, they just go for it. But in the beginning I tossed it all together.