Just want to say how sorry I am that you and Tyler are going through this and I will be thinking of her and hoping she feels better very soon. I think you have made the right decision especially in view of Tyler's age. My story:-
My Lucy had anal glad cancer which started off as a small growth but increased in size quite quickly and it was diagnosed as adenocarcinoma. She had an operation to remove the tumour plus the anal glands themselves. We didn't have chemo or any other type of drugs, the vet felt it wouldn't make a lot of difference to this type of cancer. Unfortunately we lost Lucy 15 months after her original operation but she had a good 15 months with no problems but unfortunately the tumour came back again and she became quite unwell. I am sorry to tell you this story because I am sure that it isn't what you want to hear. I am still in touch with the lady who owns Lucy's brother and he had the same thing diagnosed although he was a lot older when he got it. He had the same operation as Lucy and the vet said it would give him another year, that was 2 years ago! He is still going strong and nearly 14.
Give Tyler a gentle little hug from us.
Jackie & Cocoa