[cypher]

I agree replacing the shelves would be your best option if you can, you can buy wooden shelves that will fit in most cages & also get some free standing shelves, use houses with flat tops in place of shelves, there are quite a lot of options.
If you think she may pee on it then cardboard wouldn't last long but is easily replaceable, I would just lay a sheet on top & maybe tie it in in a couple of places with cable ties if need be, hemp mat is another option but does collect a lot of small bits of food etc which can be hard to get out of the fibres.
Grass mats are ok too if you can get them to stay in place.
Not sure what safe glue would be strong enough to attach plastic to metal bars tbh.