Whatever decision you make is the right one. As you're making it out of love.
I won't tell you what to do. But I'll tell you what I did. I went the amp route for two girls. A 12 year old and 9 year old. I had Diamond out to OSU (from NJ) for a ton of examinations to make sure she could handle it at her age. Dr. Couto said age is just a number. Diamond was a very healthy 12 year old. She did fantastic and even surprised her care givers with her recovery. She lasted a wonderful pain free 6 months before osteo hit the back leg.
Tanzi lasted 14 terrific months enjoying life to the fullest before osteo hit her back end. God I miss my Tanzi.
It's supposed to be rare that osteo comes back in another bone but both my girls had that.
While the first 2 weeks are very hard, you'll question your decision, once you're past that there's no stopping them. They just won't be able to do the walking distance you once did. And be careful of stairs. They forget they lost a limb.