Matted mess rescue

So I just bought a chinchilla off of craigslist from this woman (I know craigslist is evil when It comes to animals but the lady seemed so nice and sincere). I'm now considering my purchase a rescue. I have never seen a critter in such bad condition. She has multiple clumps in her fur on the top of her body, most of which weren't to hard for me to cut out much to her disdain. Her bottom is what I am most concerned about. It is a huge clump of urine and feces,:vomit: I am assuming this is from her being left in an unclean pen for a long time. I am so upset for this poor baby and I really don't know what to do. Is it okay if I get an electric razor of some sort to shave that mess off? A bikini electric razor was recommended to me by a close friend who uses them to trim hair clumps off of puppies.

Don't even get me started on the fact that these people were feeding her GUINEA PIG FOOD. I also spent a good chunk of money on her and the critter nation she came with.

Please help me, there are photos attached of the poor things rear.

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