I just recently won a weanling solid pinto filly. As of right now, I am doing research on feed because the food she came on is too expensive for my family
I mean this honestly, not trying to be smart Alec but if you can't afford good feed for her, how are you going to afford all the other stuff??
One reason I think giving animals to people as prizes is so irresponsible. That & the fact that many people may not have adequate knowledge to deal with the animal they're suddenly lumped with. Kudos to you that it seems you're doing lots of research at least.
She came on hay cubes, red cell vitamin and mineral liquid, and grain
'Red cell' implies to me it has iron in it, which is generally something already in excess in many areas/pasture/diets, so without a diet analysis showing it's deficient, generally best to avoid supps with iron.
As for other nutrients, good nutritional balance is vital for good health & growth. So *appropriate* supplements are probably needed, depending on a diet analysis so you know what she's getting from the basics. Horses produce vitamins in their body, so they generally don't need vitamin supps, but minerals & essential fatty acids.
I would not be feeding grain to a baby, or for that matter any horse without good reason. Grain & other high sugar/starch ingredients aren't great for horses & if you really feel its necessary & no better alternative, should be well processed, fed in small quantities mixed with forage, over a few meals daily.
the way she looks right now I am worried she is going to grow into a weird shape if I don't try to do something.
How so? Just that she is rump high or is there something particular? Yes, without appropriate nutrition, her growth & soundness can be compromised.
She is in a stall most of the day for now, but I get her outside to eat grass after school every day. So far I've read not to go to corn as a grain, read about DOD, and I'm still looking.
Get her out of that stall & able to exercise freely & living with other horses asap. Lack of exercise is seriously detrimental & lack of socialisation with other horses is also generally problematic as well as... sad.
Yes corn is the worst cereal grain, being highest in starch & hardest to digest. If you feel the absolute need for grain, oats are the best option. DOD's are mainly about pumping feed in, trying to 'grow up' young horses too quickly, and nutritional deficiencies.
She will need to be trained asap for hoof and other care if she hasn't yet. Hoofcare at her age is necessary, to ensure they grow well & strong. but shouldn't be forced. I wouldnt tie solid or otherwise force a horse of that age into anything - their bones & joints are very easily damaged.