Could you start leaving her inside, leaving the TV or radio on for her? She's probably looking for her pal when she's getting out. She might actually like being inside after she gets use to it.

I have a 14 year old Lab mix, she is almost deaf(except around the 4th of July when I have to drug her a little because she's so terrified of the noise), has cataracts, and she too has started going out of the yard and strays 3-4 houses away. She's an indoor dog and gets a little confused in the house too. I started leaving the TV on when I leave the house. My vet says she's in good health, just old.

Good luck, let us know what you decide.