It could be any number of things ranging from severe weather swings and they are demonstrating some mild colic issues to, they don't like the taste of this new load of hay and they're going on strike.
As with your own situation, anyone sitting at the keyboard is speculating.
I can say I have four horses and when I bring in a load of hay that cost $7/small square, is 99.9% weed-free but doesn't smell like green tea, it's a safe bet nobody in the barn will want to eat it.
I was only able to buy 2/3rd's of an entire season of hay in Spring, 2012. It was fantastic sweet smelling hay. Anything I have gotten in since that time, is deemed abusive to my four's taste palettes'
Time of year and/or time of day the hay was cut can change the taste, so can whatever fertilizer was used on the field, and even how long it had to lay in the field to cure before it was baled.
I have tried to resolve my picky eaters problems by feeding them timothy pellets which help in the forage department but not the chewing department which horses need to do.
My only thought for your mom is to watch them closely for any signs of losing weight and/or colic.
While I am leaning toward the fact they are being too fussy, if they start dropping too much weight or show any signs of colic, she may want to call the vet immediately.
Colic indicators could be only one or any number of these:
1. Laying down, deer fashion a lot more than is normal.
2. Biting/knipping at their sides, especially back in the lower flank area.
2.1 Lying down AND biting their sides.
3. Not drinking enough water.
4. Not passing the daily normal amount of manure she is sued to seeing from them.
5. Droppng their heads and remaining that way as if depressed or distressed. Some will even stretch their neck a little.
It is very frustrating to spend your last dollar on the best hay you can find, only to smilingly hand it out and your thanks is four sets of big eyes with ears forward saying "is THIS the best you can do? Weeeee donnnnnt liiiiiike ittttt"