Congrats on the new bunny!
You said you were using aspen shavings as bedding and also used them in the litterbox? That might be why she's confused. Since you are using aspen shavings for litter but have them everywhere else she probably thinks the cage is one huge litterbox
. Either stop using aspen shavings as bedding (you can put a towel down if you think she'd want something soft the lie on) or get a different litter (maybe a pelleted litter like Yesterday's News?). Otherwise it will be hard for her to understand the difference between the bedding and litter. My bunnies used to always push the bedding away anyways...they prefered to lie on the plastic. So I don't use anything for the bottom of the cage except a towel or something (if they want one).
You also mentioned that she keeps picking a different corner to go to the bathroom. I would block the other corners with objects so she'll pretty much have to use the litterbox. You can put the litterbox in one corner, the food dish in another, a box or other hiding place in another, and a large toy or second litterbox in the last corner. Once she's trained you can move the objects back and take away the second litterbox if you were using one.
If she still won't use the litterbox there is one way of training them that almost always works. Buy three more litterboxes and place one in each corner. You can use different types of litters in each box to see what she prefers and pay attention to which ones she tends to use more. After a few days take away the one she doesn't really use and put her food dish there instead. If she relapses you can put the litterbox back and try removing a different one. Once she's using three litterboxes for about a week remove another (the one she isn't using as much) and if possible put an object such as a hiding house there. Let her use two litterboxes for about a week and then remove the hay from the one she doesn't use as much. This means that the only one with hay is the one she prefers...also put any stray droppings in this litterbox. Once you think she's ready you can take away the second litterbox.
I hope that wasn't too confusing
. Oh, and you can use all of the extra litterboxes for out of the cage once she's free-range. So it isn't a huge waste of money, haha.
Rememeber to get her spayed when she's old enough otherwise she'll probably start leaving droppings everywhere again.
Hope this helps! It's always worked for me