yes I agree the shaving & hay take a long time to break down. It is better to start a compost pile somewhere else, if you turn it once in awhile aerating it, it will compost faster.I don't know what your goals are, and I'm fairly new to keeping chickens, but I do know a few things about composting. Wood shavings are not going to break down until the load of manure, be it chicken or horse, reaches a point where the moisture content of the mix has the shavings thoroughly damp. I know there are lots of folks on this forum that swear by deep litter, allowed to compost, and cleaned out only a couple times a year. Glad it works for them, but it is exactly the opposite of what I want my bedding to do. I want my bedding to dry the droppings out, which will knock down the odor immediately.
If I were you, I would take all the horse manure your daughter can provide and start a compost heap with it. Throw the bedding from the chicken coop on the pile when it is too saturated with droppings to dry up, and let the chickens kick through it all when they're free-ranging, instead of in the coop.