I honestly don't see why allergies are such a big problem unless, obviously, they lead to much worse (which they haven't yet, and if I wait to see if they do, she'll be too old to breed. If I breed her now, there's a chance and there's no chance. Only a possibility.)
There is always a possibility that you could be selling the foal. Life is uncertain, you cannot see what may or may not happen in the future. Which is why it is best to breed the best to the best and give a foal the best possibility to be wanted in a market full of average horses selling cheap and free. You are young, you don't even know what you will do after high school to support a hobby of riding, training and taking care of horses you love.
As far as age is concerned, why do you think your mare will be too old to breed if you wait to see what happens as she ages? She is 8 yrs old right now, coming into her prime. Wait until you finish High School and figure out how you will financially afford breeding and care of two horses for their entire natural lives.
True story. My oldest sister bred her mare while in High School, she was fortunate enough to take her mare and filly to college with her. Train her young filly through the 4 yrs of college. She had it very hard most of the time, with finances and actually have time outside of school to be with her horses. She held strong and made many sacrifices to keep her horses. When that foal she bred and raised turned 17, she was bred and had her first foal at the age of 18. Now, my next older sister, also bred a mare while she was in High School. She ended up selling the mare a year after the colt was born because she knew she couldn't afford both while in college. Just after that, the colt (yearling gelding) got collic and all the money from selling the mother went to paying vet bills. Years later, after college, that sister had a hard time finding a job and was doing temp jobs but there were long periods of not having any work. She then sold her gelding due to lack of work and she was burning through all her savings just paying bills.
All in all, your mare is still young, she can wait a few years before you start hunting for stallions. Her health may improve or get worse which would put her in jeopardy for being high risk. Yes, there is sentimental wishes to keep a part of your mare, but do not get selfish and put a foal at risk if things don't work out.
In addition, you had stated before that you weren't sure of your mare's color status. From the pedigree posted, her sire is black and her dam was chestnut. So, for your bay mare, she is Ee Aa
And a final note, you may hope to get something in breeding, but you may get something you did not want and would not want to keep after the cute baby stage ended. Breeding is a huge gamble, the only way to improve your odds if breeding a mare and stallion that possess all the traits you want, in build, temperament, height, etc.