Thank you for your query,

Unfortunately mixing feeds like NRM Equine Balancer and NRM LowGIsport are not recommended. The reason being that the vitamin and mineral premixes contained in the feeds will both be supplemented and potentially cause some over supplementation. The best thing to do is either move your broodmare onto NRM LowGIsport completely until you are happy with her condition again or stick with the NRM Equine Balancer and add some grain (like boiled barley) to the ration. Your ration below sounds like it is supplying plenty of hay and chaff but just keep in mind that a horse ideally requires 1.5% of it bodyweight per day in roughage.