How to help a horse gain weight and why is my horse doing this?

FIRST QUESTION

Hi, I need some help with helping my pony gain weight.

Her name is Shakira, BTW.

Shes kinda on the thin side, on a scale of 1-10 with 10 being dangerously obese and 1 being almost dead skinny, shes about a 4. Shes an Arab, and shes not such a good doer. She has *ridiculous* amounts of grass, (we have about 40 acres available to her, sectioned off into 2acre blocks and I move her paddock every week so she ALWAYS has the best grass. And If we run out of grass, all we have to do is mow some gorse ad ta-da! More grass.) And she gets two double handfuls (that's both hands cupped together, making the biggest handful I possibly can) and one single handful of Dunstan Eezy Mix every day. She won't eat any more feed if i give it to her. I don't have her on any supplements, but if shes been sweating hard after some hill ride I give her some electrolytes (human stuff) to get her level of that back up. She has nice energy levels, I'm a novice rider so I can't have her too excitable, but shes just right. Shes hot, and forward, but shes easily manageable.

Shes;

7yrs old.

In moderate work (ridden 3 or 4 times a week, with 1 or 2 of those times being schooling, like jumping lessons or pony club, and the rest being hacking.)

I do not think the work she is doing is to much for her because the only time she ever sweats is when i do hill-work with her (riding up hard hills) and I only do that for like, 20mins at a time. The rest of it, even after a jumping lesson where we jump like 50cm shes fine. So sweat, no puff.

She was wormed recently and I believe her paddocks to be mostly worm-free, She was the first horse to be put on them in like, 6months, and I wormed her before I put her on them, and her paddock mate when she came like a month ago was wormed first to. And I endeavor and her paddock mates owner endeavors to remove poop regularly from the paddock, so i do not think that is the problem.

This is the first year she has been on these paddocks.

This is the first year she has had trouble with weight during winter.

Her paddock mate has no problems, in fact, her paddock mate is a bit chubby and is in about the same level of work as her.

I kinda suspect that perhaps it is a problem with the quality of the grass, not the quantity and she just needs to be put on some sort of grain based feed.

I do not think hay will help because hay is just bulk and she has enough bulk in the form of large amounts of grass.

I want to put her on a feed that will help her gain weight, but wont make her crazy.

I can't just go down to my local feed store and ask because we don't have a local feed store. So I need to decide what type of feed I want first, then order it.

SECOND QUESTION

When I go to put the bit in my ponies mouth, as soon as I hold up the bridle she lowers her head and begins opening and closing her jaws, stretching them really wide and licking her lips.

I heard that foals lick there lips in the presence of older horses to tell them *don't hurt me, I'm just a baby!* Does this mean shes scared of the bit?