When do we know it’s time? 17 year old dog

My family’s dog is 17 and is for the most part a happy dog who still eats well. We’ve had her since she was a puppy. However, she’s going deaf and blind and is incredibly confused with her surroundings. She stays in bed for 16+ hours a day and the other dogs can make her snap at them when they try to play. She falls down a lot, too. My family has never had an old dog like this before and we want to know what to look for in knowing when it’s time to euthanize. Is she doing well enough that we should wait for her to pass on her own? Any other advice on how to make a blind/deaf dog more comfortable would also be appreciated. Thank you!