Digging is normal. Try a diggy box. You can build one with a box, cut two or three holes big enough for the buns in the sides, then fill it with as much shredded paper as possible. For chewing, you can throw some bits of cardboard in there so she chews those pieces. Chew toys outside of the diggy box would be a good idea too

Spaying might help calm the need, but im not sure if it will completely stop her need to rip at the tiles. You can try a custom coroplast bottom from C&C cages that might help. My buns dig in their cage when they are bored and theyve never been able to even pop a hole into the coroplast

Depends on what you use for litter. And even if, a diggy box is just a box and shredded paper so it is inexpensive I would make a second box so they dont feel like they lose their first one. I think computer paper is best. You generally want something without ink on it, and if you have to use something with ink, make sure it is soy based and that they dont eat very much of it

If you get a custom coroplast base, you would measure the bottom of their house and send it to the C&C cages people to have it custom made. That is, if they are still offering customs. If they arnt, then all you have to do is find which ones work best with your bunny house. Or get some of their flat coroplast sheets and cut out the bottom yourself I dont have to nail it down for my boys at all, but if you feel the need to then go for it. I have my coroplast just on the floor. Its slippery enough that they cant dig through it or bite it straight on (they can bite the edges, but dont care to), but has enough traction that they can still run around the cage without sliding or falling