Help improving this photo of Gus

My MIL lost her much loved dog a few years ago and it is still hard on her. I am planning on getting a proper urn for her and a sort of memorial framed photo with mementos of his for her.

Unfortunately I don’t have many pictures of Gus and this is probably the best one … however it is super dark and I tried playing around with the editing but it still looks awful.

Can someone help brighten this up and make it a clearer image?