Oh Parmela, this is the hardest decision in the world... and been there, done that, so I sympathize with you having to think about this decision.
Unfortunately most of them do not just 'die in their sleep' or fall over, and a decision has to be made about their quality of life. She may begin to give you other signs or she may not... but if she has not bounced back from last winter, even with a heated barn, I fear that this winter is not going to be any better.
I had an old mare that was given to me for a retirement home- she had her own pen next to my stallion just for company. She was 25, had been a pasture broodmare on a couple of big farms, so was far from being a pocket pet. She had arthritis and could no longer eat hay, even just leaves, because she would choke. She got free fed a complete Sr. Feed because it would take her all day just to nibble and eat breakfast. Her weight stayed decent and her coat looked good, and her eyes were always bright.
The desert here doesnt get too cold in winter- it can freeze nights, but is certainly not like other climates, so I didnt have an enclosed barn. Her arthritis was a little worse- and I could tell that cold weather bothered her but the year of her 30th birthday, came home to find her down and she had to have help to get up. She was fine the next few days but then it happened again, and this time I could hardly get her up and the poor mare had been down a good part of the day. She looked at me as if to acknowledge it all, but her eye had a different look in it, and I could tell that she had been scared, laying there alone and not being able to get up.
With that happening, I knew she would end up colicking or something worse would happen..... and couldnt see her going through that. I made the decision then that it was time.... it was just getting worse and there was no turning back and it hurts me less to have to put one down than to see them scared, hurting or not enjoying life. I just cried and cried, but it was time.
I hate 'playing God' and hate having to decide when a loved part of the family has to go, but it is part of the responsibility, as we all know, of caring for all of these wonderful creatures.
I agree, that perhaps if you are questioning it, you may be answering your own question really.... Hugs to you in what you decide to do... no judgement here- like I said I think this is the hardest thing for anyone who loves animals to do. And it never gets any easier.
I would really weigh how she is going to do stuck in a heated barn all winter without being able to enjoy 'moseying' around outside, or being able to get around much, etc... And even the heat in the barn may not be enough to keep her going all winter. If she has not done that well this summer, her body is beginning to wear out now.