Balancers are usually a combination of vitamins and minerals together with a protein source, probiotics/prebiotics and sometimes some oil as well.
Originally they were designed for growing youngstock whose protein requirements are higher than mature horses, and can't always be met with hay alone. Traditionally, cereal feeds were used to boost the protein levels of the diet, but this method sometimes provides too many calories for native types and also can lead to horses growing too fast which can cause limb problems etc. The concentrated balancers allowed youngstock to get plenty of protein and all their vit/mins without giving lots of cereal feed.
Since then balancers have been marketed to a wider audience. Horses that are receiving the recommended amount of a cube or mix don't need a balancer, because the cube/mix contains similar nutrients to a balancer, just not in such a concentrated form.
So yes, you can feed a balancer to your 2yo filly, but don't feed it alongside an already supplemented mix or cube.
right so at the moment she is on paddock gold (mix) and hi-fi original with sugerbeat so if i took the mix out and put her on the feed balancer would that work
That's why I said it is probably best to give them a ring and find out what is best for your filly - you can tell them her size, breeding, whether she is a good doer or not, any problems you have had, and they can suggest the correct one.
The best one for a growing horse would be probably the comprehensive; I think they do a stud one too. Their labels are actually quite self-explanatory, and if you don't want to ring them, email them or read the info on the website. They come back to you very quickly by email.