That haybag lasted about a day and a half with my two horses, with extra piles of hay on the ground, so not being abused because it was the only source of hay. Not worth the money, IMO.
I made my own nets, baling twine and a couple of hours work. It's free and I'm the one deciding on which size I want. Important is that the holes are not bigger than 2", so it remains a slow feeder and no BAREFOOT hoof can get caught.
If you have a steady source of hay, it would make sense to get it tested for NSC content. If it doesn't make sense because you buy your hay as you need it, you'll have to guess rather. For horses prone to founder overall NSC shouldn't be higher than 12%. Good grass hay has around 13%. So washing the hay might be necessary to get excess sugar out. It's easy, stuff the net, submerge net for 1 hour in water, discard water, hang up net.
I strongly suggest giving either a vitamin/mineral supplement or a ration balancer. Mineral licks just don't supply enough. A magnesium supplement will help her also, exciting new research about that.
My personal experience with slowfeeder nets is that they self limit hay intake, mine went from 25lbs to 15lbs daily. I weighed what went in and what was left after 24 hours