She should have 10-14kg of hay per day, so if she's having hay in the morning too then she will only need half of that morning and night. :)

 That should say 10kg!

i would say about 4 sections, or if she has it dry as much as it takes to decently fill a hay net. this prolongs her eating as well as she has to get a decent mouth ful. or another thing is if you get a hay bar and give her as much as it takes to fill it up (obviously not stupid ammounts)

or you could experiment over the next week with different ammounts and see which suits her best,. hope i have helped :) x