Is OTHER wrong in the post ? POST : I'm expecting to be an a-hole because it seems VERY petty and I feel like I need to hear it from someone else to validate my feelings.

A bit of background: I'm staying at her house until I get enough money saved up to move out and do whatever it is I want to do. We get along exceptionally well, me and the family, and I'm basically a second son to them. I help out whenever possible (biggest thing I'm doing for them is assisting her husband with renovations at his MIL's house, which hes been needing for a good while) and do my best to be a good house guest. From my conversations with them, they enjoy having me over. Specifically relevant to this story, however, is that they bred a dog for me 3 years ago and so I live with them and my dog, who they assist in caring for along with 2 other dogs.

So I got my dog a $180 pet bed. Why? He tears up any and all beds he gets EXCEPT this one because the cover is durable. So I get a text this morning from her saying that the covers zipper got stuck and she decided to still put it down on the ground, leading to my dog eating a good chunk of the corner. I didnt read the bit about the corner getting chewed, so I was absolutely chill about it, figured it wasnt a problem, and called the pet bed sellers who sent me the warranty email and told me that the cover should be replaceable, all they need is a picture. I go downstairs to get a pic and I notice that the bed is tore up...still usable, just that the corner is now opened up and missing a bit of volume. I call my friends mom up and ask her what happened and she tells me that she decided to put the bed on the ground knowing that the zipper was broken because "it was so cold I had to". The thing that frustrates me about this is that she knows my dog chews up all the beds we get him (she had gotten 2 beds recently from Costco and I had gotten him one from Target before getting the new one...all of them he tore up) and she also knows that the beds cover was the SOLE reason why this bed has survived for so long without damage, so to just set it down knowing that it was busted and hoping for the best, in my opinion, was stupid. My other reason for being upset is that we didnt split the bill on this: I paid for the entirety of that bed. I dont have much money as it is (currently looking for work, just recently got let go from the military), but she was going to go out and buy another bed that was guaranteed to get eaten up, so I wanted to eat that cost for her and just get a bed I know he wont destroy, so to hear her be so nonchalant about the damage (her reasoning is that the warranty should cover the bed as well, when we dont know if it will) was pretty upsetting when I made a decision basically for both of us (she insists on taking care of the dog alongside me, however I can see someone pointing out that I'm an asshole for even having her help me care for my dog at all). 

I really dont have much room to be upset, considering they feed me and provide me shelter and are very loving and caring towards me, but I still FEEL like I have some room to be upset, as this was, frankly, a very stupidly easy to avoid situation that she could have seen from a mile away, and my ideal resolution is to have a conversation about it and plan out what to do if it happens again. Nothing crazy. But I was pretty frustrated talking to her about it over the phone and I just wanna know...AITA for being upset over this, and regardless of whether I am or am not, what would be the best way of addressing this problem?

TL;DR: Friends mom, who I'm living with pro bono, accidentally facilitated events to occur that wound up having my $180 pet bed get eaten up by my dog when the situation was completely avoidable and I'm upset about it.