horses have evolved to be trickle feeders - the saying "eat like a horse, little and often" didn't come about by chance! What sort of bedding is it on, at least if there is some straw in there he can pick.
Even giving "large feeds" is of little benefit except to us feeling like we are doing something as the horse can't digest it quickly enough and it gets pushed from the stomach through the intestine and out again so quickly the nutritional benefit is lost - and don't get me started on overfeeding grain and starch!!
The sooner people stop feeding what the feed manufacturers tell them they have to feed and start feeding what the horse actually needs the better off the horses will be.
Fibre is the answer, preferably long chop and lots of it - dry. Then they have to masticate properly instead of chomping and gulping - means they take longer to eat a bucket and it is slower to digest hence they get the benefit from it and you find it saves you money and time in the long run.
Both mine have haylage available all day then pony gets an offering of hard feed while TBx has one hard feed a day (not v big tho).
You should def say something to her! One of the last full time liveries we had was like that and her horse ended up with stomach ulcers and several episodes of colic before she realised her mistakes.