First of all, welcome to the forum!
I am currently training my 15 year old paint mare barrels, poles, and speed events alike.
Strictly because of your horse's age, have you ever taken her to a vet for a full lameness evaluation? Speed events are very hard on a horse's body, especially when they are a little older. To keep them in good running shape, and to prevent any problems, I routinely have my horse's checked by a good vet.
Also, make sure her teeth are examined at least once a year (For good dental care) and it is always a good idea to have them checked by a chiro.
I started her last year and for not knowing anything about it previous to purchasing her, she caught on quite well winning me a Reserve Speed Champion title.
She doesn't have them perfected yet but is definitely coming along; however, I recently ran her and she was very very hot. I ran the pattern and she continued to run and turn and stop, but I didn't feel like she was "listening." Wasn't sure if maybe I just wasn't used to this enthusiasm or if maybe she was being disrespectful.
If she was not listening to you, then she's not listening to you. Disrespectful!
It's always a very fine line when dealing with gaming/barrel horses. You want them to have that extra "fire" in their feet, but yet you need to always maintain control. Always.
Were you at a show with this episode, or were you at home?
I would slow her back down. Get control back. Get her listening to you. If you need to, enter her at a show but make her take it slow. It is much easier to "head off" a problem ahead of time, than to try a fix a horse that has already developed bad habits.
Also, do you do any slow events with her, such as western pleasure, ranch horse, reining, etc? That would be good for her mind too, so that she learns it isn't always run-run-run when she's in the arena.
I do every single event with my horses so that they learn when it's time to run and when it's time to do something else. They don't get "on the muscle" until I give them the cue to do so. I am very specific with them so they learn to know exactly what I want and exactly what is going on.