Can you get pictures of your mare?
True free choice QUALITY hay is the real KEY. By free choice I mean, I offer a second cut round bale 50/50 grass alfalfa and when it get low (approx 150-200 pounds of round bale left) I place a new fresh bale out. Rule of thumb, If I wouldn't put the hay in MY mouth, they don't have to eat it. (Most people think free choice, round bale and they have to eat it until everything is gone - truth is the last 100 or more pounds is nasty and they shouldn't be required to eat it. Or free choice with squares, they pick threw and leave a lot. Free choice means WASTE a LOT of hay!)
Secondly I feed a mixture of a complete feed Senior feed, soaked beet pulp and/or soaked alfalfa cubes, a little rice bran, Nutrena Safechoice or another high fiber low sugar feed.
Thoroughbreds require something like a mix of this that amounts to literally a 5 gallon bucket TWICE daily. About half for the other breeds.
If you're not already, get free choice hay going first of all.
Secondly the feed you are feeding is good but you'll need to offer more. Three "cups" of beet pulp is honestly not doing anything, literally might as well not be feeding it. Two-Three QUARTS twice daily is more appropriate.
Depending on your scoop size on the Senior feed? I would feed TWO 3 QUART scoops of Senior feed twice daily. With the 1 3qt scoop soaked beet pulp. If you can, 3 cups of rice bran as well twice daily, maybe ad a 3qt scoop or two of soaked alfalfa cubes fed separately (like a "lunch snack"). Up her feed slowly over 3 or so days to this amount. I typically just start my rescues out right the heavy feeding right away and I've never had colic issues but I suppose I'll suggest a slower increase over three days :)