Oh poor thing! Sure she's pregnant. Now if there was her nestbox rabbits start nesting around day 28 and usually kindling on day 31, well it can be between day 27 and day 36, anyway you don't know due date just it could be very very soon.
Since you gave her a nestbox and she has some privacy there she'll be fine, it is important that she had unlimited hay and a plenty of water she will drink a lot when it begins. I am not too sure about food, you don't know what was her usual food? It is important not to overdose well she needs unlimited pellets while nursing but now because you will have to change it so quickly it could be shock and better give her in small doses and see if she eats quickly, she is maybe hungry as well. If she wasn't getting enough food during her pregnancy there is possibility that some of her kits can born deformed or weak, so don't be scared but maybe they will be all good, maybe they were fed okay let's hope for the best.
She won't need your assistance it is best to leave her maybe even cover her kennel with a blanket so she can feel safe. Is that her nestbox in photo? She will need more hay, lots of hay so she can build a nest maybe you can help her and you can pluck some fur from her belly around the nipples and line the nest with it. The box should be not too big because she will feed her kits she'll stand over them put her legs into corners for stability. Here's a short video how to prepare a nestbox might be helpful.
She uses a very large box because of her rabbit is a large breed but she explained everything clearly so just fill your box with hay and put something underneath to absorb the moisture or just to let the moisture go through they will need it for about 4 weeks so basically your kits will pee and poo into it you won't see poos they will be very tiny but you want them to stay dry so just be prepared. There are plenty more videos on youtube just search for rabbit nestbox
She will probably kindle in night time when nobody's watching so just check her nest every morning and keep us informed, any question just ask!