I see a very composed and balanced rider on a horse that seems mostly happy , composed and balance, too. She is 20, so modify your expectations accordingly, and she has come to this sort of training late in life. With that in mind, you should be very happy with how far you have come.
It is true that you might be able to get a littl more ump out of her, but you also stand to get her irritated and unhappy. Unless she is really holding back, I would not jab her with spurs, but rather encourage her more forward , little by little, rewarding her occasionally by allowing her to stretch forward and go on the buckle (very loose rein). She has given a lot into this equation, so push it slowly.
With this in mind, and seeing how nicely balanced and quiet you are, you might work on getting her to stretch forward at a canter and then to collect her back up. Working on longitudially lengthening and shortening your horse, all slowly without haste or pressure and keeping exactly the same easy rythm.
You have a lot of potential as a rider!
This horse really just loves to work. As I started riding her more, she actually was willingly going into a headset and the trot and sometimes at the canter. So I decided to help her a bit with that and teach her an english headset (: She really is the sweetest horse. Im not really making her to any of this, she does it very willingly. She was a western horse in the past, and she's a bit dead at the sides, so I use some prince of wales spurs. Not anything extreme, but enough to get to the point. Especially since she's probably used spurs before we got her. I used to ride on very loose reins, but im trying to get her into more of an english style. I understand she's old, but she really doesn't act like it at all! That soudns like a good idea. I came up with the jumping just to find something else to do rather than going around in circles working on a headset. I was also thinking of dressage. Of course none of this is competitively, but just for fun and to mix things up a bit (: