Range for Tramadol is 2-5mg/kg every 8 - 12 hours. So for her weight, 150 mg per dose is at the high end.
I agree, that seems like a lot just for arthritis. When DesiRay (85 lb) was having his nail problems, he did ok on 100 mg, every 12 hours.
It never phased him with side effects, but I had a 60 lb (non-grey) a few years ago with horrible hips; she took 50 mg twice a
day. Toward the end, I tried to kick the dose up some, but it really knocked her for a loop. She couldn't even get up, just
wanted to lay & sleep; when she did get up, seemed "out of it."
Good luck. Hope she's feeling better.