So you want to shoot 350 yrds, getting neck shots forinstand incapciationyet compromise on the chambering???

If I needed such on-target energy to drop the animal in it's tracks, I certainly wouldn't compromise in the chambering. Keep the shots closer and stick with a .30 cal (7mm minimum) and I'd have little worries.
Good chance an 8yo is fairly small and having a rifle as you seem to need I think would be too much for her. (what has she shot thus far?)
As for said neighbor being an "@$$ hole". Is it simply becasue he won't allow folks on his property? Having been there, done that,I can certainly understand his side quite well. Allow one and more and more abuse the privledges. Not long before a few ruin ot and there's such fencelines disallowing access.