AITA for not paying when I lost a bet?

My gf and I have been living together for about a year and one of our main arguments is around my boxer mix Max. She thinks she’s a dog whisperer because her dog Jupiter is basically the perfect pet and that I’m a lousy dog owner. I think it’s because she has a border collie that just train themselves. She hasn’t developed any of the normal routines that dog owners do like put their shoes out of reach or never leave food unintended and gets angry everything she pays for it. She left a grilled cheese and Max helped himself. She was pissed and told me I was the asshole for not training my dog. I argued no dog is going to turn down a grilled cheese and after arguing around we agreed to see if Jupiter is that impressive by leaving steak in front of him, leaving and seeing if he sneaks a bit. She said $100 was on the line and I said sure and then said it was too low and said $1000 and I admit I agreed because I didn’t think it was possible for me to lose.

Well we cooked steaks and put 2 on plates near Jupiter and left. She reminded Jupiter to leave it and we left a phone to record in case he licked but didn’t eat it. We left for 5 min. Jupiter didn’t even seem tempted. I was honestly shocked I didn’t think it was possible. I admit I’m kind of impressed. Max would have eaten it immediately. But now I cannot afford to pay the $1000. My gf wants me to pay it to her in increments. $200/month until I paid it. I’m trying to talk her into lowering the price. I already paid her $100 but she thinks I’m the asshole for agreeing and then backing out. I already admitted she won and I only make $21/h, I’m not rich. I think she’s getting a bit greedy and smug from winning but AITA for trying to go back on paying the entire $1000 after losing our bet?