She is the perfect age to train on a harness! (NOT a collar).

I have seen very happy cats on a harness and leash that are tied to a large screw in the ground(like dogs have). You just have to be sure that the leash is not long enough to tangle around another object, like a tree.

And I have seen cats walking happily on a harness and leash. Might be an option for you.

My one cat was a wild outdoor one, my other guy dumped, but obviously used to being outdoors.

They are happy inside - they have toys and me and each other! In a second floor condo.

The risks are too heartbreaking otherwise.

I vote for INDOOR - with toys and attention and love.

hugs
Catty1