Not the right feed and definitely not enough of it, I would change the chaff if you can or add some sort of conditioning feed with micronised linseed, I would also try and feed 3 feeds a day if you can.
If she does well on it I'd go back to the Speedibeet, it's a great semi forage "hard" feed that's a bit out of fashion at the moment but does work well! I'd also add a mug of micronised linseed - that's a good option for any horse in winter tbh.
My two live out and get nothing bar half a scoop of cheap mix so I can give them their linseed, plus Pro Earth balancer. The Dales is on a tri aminos trial as well. No hay as it's a big field and I'm still struggling to feel ribs (flipping natives!).
Fwiw at 22 I'd do a cushings test anyway if weight has dropped.