Trotting for an hour every day is definitely way excessive. I strongly suggest that you cut that down to less than half as much. I would never do that much with my horses, and they aren't even that old. I have also been told by a vet that the trot is the highest impact gait on horses' joints, so it's probably not too good for old bones to be trotting for an hour every day.
That isn't to say that you shouldn't be riding her at all. Walking for an hour or more at a time shouldn't be too hard on her, and going up and down slopes can really help with muscling.
Something to keep in mind is whether this mare is getting enough feed to put on muscle and keep up her weight. Older horses usually require larger and higher quality rations. She does look like she could do well with some more meat on her bones. If she's not getting enough protein and calories in her diet and you're working her this hard, it really could be detrimental to her. I suggest that you research horse feeding and nutrition thoroughly on this website: Horse Nutrition Explained
The biggest thing is just to pay very close attention to how your mare acts and moves. If she seems lethargic or pins her ears and makes a fuss, she may be telling you that she's uncomfortable. Also, if she's moving very stiff and jerky or unevenly, it is a sign that she could be uncomfortable. You need to pay attention to that and heed her warnings.
As a side note, she is not performing Spanish Walk in your video. From what I can see, she's just picking up one front leg and stretching it out. A Spanish Walk involves picking up both front legs and literally walking forward with their movement. The Spanish Walk is also something that the rider needs to be intentionally asking for, not just sort of randomly getting.