[Shotgun93]

2 flakes a day? Is she on pasture? That really isn't a whole lot of hay, which might be attributing to her weight issue, as well as her colic issues. I would bump up her hay to start with.
Like JB said, the BOSS is a good suggestion. A good quality pellet feed might help, but I would stay away from grain. But, with upped hay, the BOSS and bran, it might be enough to keep her weight at a good level.

[Twisters]

ok, she is in a small pasure, it does have grass.

so 3 or 4 flakes, and pellet feed...?

what kind of hay is in the pellet feed?

[Shotgun93]

A horse needs an average of 2% of his/her body weight in forage - hay. For most horses that's between 20-30 pounds. Some easy keepers need less, some hard keepers need more. Some horses don't digest all they need from hay, so they need more than normal.
A good bet with a hard-keeping horse is to offer free choice hay and monitor their weight. If the weight goes up too much, cut back on hay. Adding hard feed on top of that isn't always neccessary and it really depends on how much work the horse is in, and what their overall health is.

Sometimes they only need a ration balancer, free choice vitamins and minerals and hay (and the phyllium in your case). If it were me, I would start with the that and see where her body condition went. If you are happy with the bran, you can continue to feed it, but do know that research has shown that it really does nothing to fend off colic. It does well at adding weight though. To add weight, I would add BOSS to that. If that doesn't help, then I would start looking into a pellet feed.

Pellet feeds vary greatly, some are excellent quality, some are not. The lower end feeds don't have a consistant ingredient list, something that can be detrimental in horses that need to have a specific amount of a certain vitamin or mineral, like in your situation. Higher end feeds are much more specific about their ingredients, as well as consitant. Most don't state what type of hay, if any, they use.
I feed mostly Dynamite products, which are good quality. I also feed Nutrena's SafeChoice which I have had a lot of luck with. Generally, some of their feeds aren't up there with high quality feeds, but Safechoice works well for me. Triple Crown is also very good.
Sue B would be the one to go to for exact calculations on ingredients and balancing out your horse's potassium needs with everything else.

[AlPadrino]

Mitavite Pro sport would be good but i dont know if you get it in the u.s?

[JBandRio]

Originally Posted by Twisters

ok, she is in a small pasure, it does have grass.

How small, and what does "it does have grass" really mean? I see you are in Ca. For the most part, this time of year means very little grass unless you stockpiled a reasonably large pasture starting in late Summer to be grazed as "hay on the root." If your grass is less than 3" tall and getting shorter, that isn't providing enough calories - busy food yes, calories in quantity no.

so 3 or 4 flakes, and pellet feed...?

You need to weigh your flakes to get an idea of how much they weigh on average. You need to feed by weight, not # of flakes. The average flake weights about 3lb. Some weigh in the 2lb range, some in the 4lb range, and rarely in the 5lb range. If you're feeding 3-4 3lb flakes, that's 9-12lb, and if she's 1000lb, then that's not nearly enough. If she weighs 1000lb (or SHOULD weigh 1000lb), you want to be feeding 20lb, or more if she'll eat more. If she's small and should weigh 800lb, then you want to be feeding 16lb or more.

That much more hay may be all you need to get weight on her. The BOSS is a great addition and contains potassium which she apparently needs.

what kind of hay is in the pellet feed?

Depends on the pellet. Many contain an alfalfa base, some contain a grass hay base, and some are based in beet pulp. I just simply would not go to adding a grain right now until you get the hay increased and determine if that's enough for her. She does need vitamins and minerals though.