I'd start with 50 grains, She'll buck pretty good with just the 50 in her.
I have an ENCORE 209X50 15" PISTOL that I started with about 80 grains and then realized right then that there was too much to try and hang on to and still hope to hit something with it. I backed it down to 50 grains of Goex FFF and the recoil is manageable now and it shoots really good for me. I am sure that 50 grains will run through a deer at 50 yards.
Let us know what you think after you shoot it.