How good is your pasture? I see you are in QLD, are you still in fairly drought conditions, or have you had a good spring like us down south so have more feed? What condition is your mare in? Is she an easy keeper, hard keeper, etc? Has she ever foundered? Tied up? Is she insulin resistant?
I do PC, mustering, shows etc. on my horse, and he is getting Speedi-Beet (dried beet-pulp), Copra (coconut meal), and oaten chaff. I'll soon start supplementing him with Equilibrium, Vit E and Selenium supplement and a salt lick.
I'm a big fab of not feeding grain. A lot of research is showing that it is healthier for a horse to NOT be fed grain, or commercially produced 'sweet feeds' as they are too high in 'NSC' or 'non-structural carbohydrates', which are now beleived to cause founder, tying up, insulin resistance, etc.
Yep, we call it lucerne and it's the main hay fed to horses in AUS.
^ Okay. That means that you will need to supply a lot of forage. A good way to keep her forage intake up is to put a round bale of meadow/grass hay in her paddock and let her just have it free choice. For energy, I suggest lucerne hay along with a hard feed and a supplement. I'm going to recommend feeds that have no grain, see my above post.
Speedi-Beet is a good 'bulk' feed that also has a bit of energy. Copra is very high in oils so is a good source of 'cool' energy. Micronized lupins are also another good feed, though I have never used it so don't have any advice. I feed Speedi-Beet as a base, and add Copra to my main ridden horse depending on the amount of work he does. The high oil content is also good for general coat and hoof health. If you have no pasture then I can guarantee your mare is lacking in vitamin/mineral intake, so a supplement would be a good idea. There are tons out there, some of the most popular are Equilibrium, Livamol, etc. A salt lick is always good to have in the paddock, horses will self-regulate the amount they need. For added energy as well as bulk, you could give her a biscuit of lucerne hay daily as well.
I think you should let your horse decide if you really need to revamp things; if she seems to have alot of energy, and recovers well from your work outs, then chances are, she doesn't really need things changed up. If you feel you need to add something just add some more hay to replace what she's used working out.
If she is lacking in energy and seems to 'droop' after a workout, rather than recovering well, then you may look into a good feed mix to help her out.