Wilma, I could win the Olympics worrying contest! Worry and anxiety nag away.
I was very close to my parents. I loved them dearly. When Dad died I as the only one nearby to keep an eye on my Mum. Although she was frail in later life she was such a cheery soul and good company. When she died I was bereft. I missed her so much. (Still do.)
You know what's happening Wilma? You are worrying about future events now. Worrying now whilst your Mum has company and is active is spoiling your life, and in effect, your relationship with your Mum.
Now is the time to enjoy her and feel blessed you have her. "Never worry worry till worry worries you", or words to that effect have had to be my guide through adult life because I can fret about so much. It seems to be in my nature. I do know how you feel.
The time to worry about your Mum is when - well, when you really do have a situation to worry about concerning her. Try to remember that. You will cross that bridge when you come to it, and only then. She may have many good years ahead of her, who knows, so make the best of now.
Try not to think of what will happen. Death is inevitable but right now your Mum has a good life, even though illnesses or bits not working properly tend to plague us all one way or the other as we age.
Live for the day. You'll be a better daughter to your Mum that way. Just hug her when you leave her, every time, and know you have always done your best by her, and always will.