Being very slim in that age is probably nothing to worry about, as long as she eats well and have good energy. My 12 year old has always been a toothpick and very active.
You may try the enzymes again; they might have a say in it.
Now food has good zinc lozenges I used before my kids could swallow capsules. You may check her iron levels, as zinc and iron competes in uptake; they needs to be balanced.
Magnesium citrate / malate as a powder is easy to take; mixed in juice or food.
Almond milk is great as the magnesium-calcium balance is much better than in milk
I have tried the mag oil, but found the powder (later capsules) easier to administer with kids.
You may add some boron to the regimen; as this balances the mag / calc. It has worked great on the adhd cases of mine.
A key mineral IMO.
It will be a lot easier the day she can take capsules. For me magnesium has been a blessing, but it took a long time to find the right supplement, and to get the levels up.
I know there has been some success with omega 3 / fish oil and adhd. But I dont know; giving her the fats that you do seems good enough. Best of luck to you HH and your daugther, keep us posted.