Whisper I honestly admire your courage.
I can't imagine having to make this decision. If you think the horse is too much for you, then you may be on the right track to sell her. It all depends on what you believe you can do. If you don't think you can handle her right now, then I would definitely think hard about selling her. Mind you, that does not mean you have to just let her go to anyone. If I was you and IF you decide to sell, I would be the pickiest person on earth (and I would make them sign a contract). I would only sell to someone who would love her and train her right, someone with plenty of experience, maybe even the trainer?
She may not make a perfect barrel horse, but you really need to weigh your options. Is that a deal breaker for you?
But you should know there may be some other options out there for you. Do you have any friends that are more confident than you with your horse? Maybe they can give you lessons. Or maybe you can have your trainer give you lessons at your place, and teach you how to help both you and your horse. You could have a horsey friend ride her and help teach her if you have one, they are way less expensive than formal trainers
If you really don't want to sell her, then don't. Honestly, you can save money up and train her later. Do what you feel comfortable with her and don't pick a battle you can't win. Just being your pet though is not letting her waste away in my opinion. In your care she is well fed, watered, and obviously well taken care of. She is still young right? I couldn't afford training with my first mare, so I did what I knew I could teach her well, and I saved up and then put her into training. I also worked part of it off..
My point being, NEVER let ANYONE tell you that a horse always wastes away because it isn't being ridden. Yes they need a lot of attention, but she has her basics. Keep working on them and perfect those ground manners while you save up. After all, ground work can always be improved