She is one of the bigger dairy breeds, so should hopefully give plenty of milk. Personally, I would start as you mean to go on, which would ideally be milking twice a day, morning and night, at roughly the same time (although obviously if you are a bit late or early, no matter!)
I would not go back and keep trying through the day, this will probably agitate the goat, who will think "oh no, its her again!" Is it just you are finding it hard to get any milk, or is she moving about while you are trying to milk. If she will not stand while eating her food, let her eat her bucket feed, leave it a few minutes, and then, fingers crossed she will chew the cud, and let you milk.
How old is the goat? Is this her first kidding? First kidders are not ideal to milk at first. Don't worry, you will get there in the end, and be able to milk her ok. Is there a goat keeper nearby, or even maybe an older farmer, who can milk by hand, and has milked a cow (saying an older farmer as the young ones will only be trained to milking machines!!) Just thinking they can milk the goat out for you, and show you exactly how to do it.