I have been thinking that my horse may need some extra calories (instead of just grass) due to being worked almost every day. She is not "skinny/underweight", but she is looking a little "weak"
Can you describe what you mean by 'weak' and if she's not underweight, why do you feel that extra calories will be the answer, esp when the vet said she is fine? Nutritional imbalance, body issues, atrophy, etc could be some alternative causes of 'weakness'.
She is just getting 8-16 oz of a ration balance right now with good quality protein, so I know it's not a protein lack.
Not sure what 'super protein' might now be available, but only 8-16oz of 'ration balancer' may NOT provide her with adequate protein, if she's not also getting some elsewhere. Not that horses generally need high protein & the amount she gets may well be enough, but it is no kind of given that she gets enough from a small amt in ration balancer.
I don't really want a "hard-feed" (like TC Complete or whatever) and I don't just want to feed her oils. I was thinking about alfalfa, beet pulp, timothy, etc.
Why don't you want to hard feed, or add oil? Alfalfa(chaff) and beet pulp are 2 common ingredients in 'hard feed' so I'm wondering, what is the 'hard feed' you don't want to feed? Fat sources are generally preferable to carb/sugar/starch sources(like grain) for added calories.
I think alfalfa is generally a good feed additive/part of forage for most horses, it's low sugar, high energy, high in protein, calcium, etc. But the... forget the term, plant based hormones - in it don't agree with all. Beet pulp is a good low sugar alternative/additive to forage, to bulk up a ration & reduce the amount of sugary grass/hay the horse may otherwise eat. Timothy is a common type of grass, so without specifying otherwise, your horse may well already be getting this, in hay & grazing. What is special about Timothy grass that you thought about adding more of that?
She is a relatively easy-keeper; I just need a little more "umph" besides just grass.
Again, if she is an 'easy keeper' what makes you think it's calories she needs more of?? What 'umph' does she lack? Energy? Agility? ...? Perhaps it's a body issue or something else, that makes it uncomfortable for her to 'umph'.