My cage is 80% wood 20% plastic toys or accessories. The two baths are plastic, they have a plastic bell ball and some other bits. Mine don't touch plastic, even my baby, I put that down to how many wooden toys and treats they get!
Some degus love plastic, some won't touch it, it seems. We got a glass bowl for a bath, and leave it in all the time. At first we had one of those glass candy-store type canisters, the ones that are shaped kind of like a fishbowl but tipped sideways a bit, so that the sand wouldn't just fly out. Then I found a glass pumpkin-shaped bowl, so that the top rim is curved inward, again, to help keep the sand in the bowl, and we use that, now. They do tend to drag some wood chips in with them, and sometimes poo in it, if it's not also too soiled with pee, we just sift the debris out and add some fresh stuff, they seem to like it the way they like it, not perfectly clean and fresh.
As for chewing stuff, there are many woods that are safe for degus that you may be able to collect locally, as long as you are sure it hasn't been sprayed with chemicals (or is right alongside a busy road getting doused with exhaust fumes). Apple, pear, cherry, beech, birch, willow, hibiscus (rose of sharon) are all good, I used them in my cage. Then, there's a list of others that are safe also, I think that the more common ones like oak and maple are now okay, they used to be considered suspect, but check the lists, or maybe someone else here can give an update? You can put bigger branch pieces in as something to both climb and chew on, and little twigs for chewing. The more choices they have to chew on, hopefully the less they will chew on something you don't want them to. (But not always. Don't ever let them figure out your real intent.)
That's kind of the crazy thing she has sticks and chew toys plus her house to chew on but she seems fixated on chewing the plastic instead. Also I noticed on the first day she eats her own poo on occasion so I did some quick research to make sure nothing was wrong and found out it has something to do with the organisms living in her intestinal tract.
Yes, they make two different kinds of poo. One kind is hard and dry, those they drop and leave. Then there are the special ones that are soft and moist, and they re-eat those (called "coprophagy")for the additional nutrition they can get from them. Weird, but evidently good for you if you're a poop eating rodent.
As for the chewing plastic, degus like what degus like. Who knows what goes on in their tiny little heads.
I have two double critter nation cages, one for boys one for girls. It is really the best cage available in the US. My girls chewed through one plastic tray and I ordered a metal replacement pan from Bass Equipment (.com). Its custom fit really a great upgrade ($50). I cant say enough for the critter nation. I think you will really enjoy it.