If your cat is peaceful, happy and is not burdened with her condition, you can feel comfortable with letting her die at home.
As for euthanasia, that is a decision that only you can make. You have to decide how far you want to go with this.
This is a pretty tough question to answer and I really think that it's a personal decision that you must make.
I counsel people on this topic all the time, though, and I can tell you what I would tell them.
You should choose three things that your pet loves to do. It might be chasing a feather wand, eating treats, being scratched behind the ears... As he gets older or, maybe, sicker, he will cease being able to do these things that he loves. When one thing is gone, like chasing feather wand, it's ok because he might take up a new activity like sleeping in front of the fireplace. However, when you can no longer find even one thing that he loves to do, it might be time to reevaluate the situation.
As far as guilty feelings go, you should not feel guilty if you decide that your pet is no longer living a happy, content, productive life and you help him to go on to a better place. You have to remember all the good times that you have had with him. We are lucky in that we are allowed to help our pets to move on. Sometimes I wish that we could do the same for people.
I hope that this helps you to make your decision.
Let me know if you have more questions.