There just isn't a market for the majority of horses even if they're professionally trained unless they are truly exceptional.
Sometimes younger folks get carried away by the idea of breeding their animals - I know I did as a kid. When you say "the foal will always be mine" to assure others that it will always be cared for, you aren't being realistic. Lots of things can happen - circumstances change over 25 years. You will find yourself with limited resources, the withdrawal of parental support, perhaps health problems or tragedy. Priorities change when you are young and you may want to travel or live where it is expensive to keep horses.
I like this mare - she looks like a sweet girl and a decently built horse. I'll bet she makes a terrific horse to train and learn on. Do her a favor though and don't breed her.