OMG, if my friend did that, I would seriously think of taking all the pee and poo stained towels over to her house and throwing and smearing them all over her carpets.
I am furious, and it didn't even happen to me.
I cannot believe this person can even consider herself a friend. And to give you no explanation, not even a lame excuse? Unforgivable. Basically, she is guilty of animal cruelty, and she needs to think long and hard about what she did.
I don't know what she could have been thinking. She obviously would know that he would have to use the bathroom at some point, even if she forgot about the food and water. Or maybe she thought if he didn't eat or drink, he wouldn't have to go? Does she have some grudge against you? This totally boggles my mind.