I have bred and raised many foals and the only mares I ever had a problem with were older virgin mares, 3 times, 3 mares. I have bred older mares, up to about 20, but they had foaled within 2-3 years. One problem was getting them in foal, pasture breeding was the solution all 3 times.
I personaly don't like fall or summer foals, had fly strike 1 time and the flies and heat and older grass just seem to be a detriment to my ways of doing things.
Maybe wait , or have the mare vet checked to see if she will breed or can use some assistance from vet in the form of drugs to induce heat. If you can get her bred by end of july, she would have a foal near the end of june which ought to be ok.
Actually, decent bred foals can be bought pretty cheap in the fall months, cheaper than all the expenses of stallion fee, mare care, etc., plus you widen the choices of what you might want? I have bought several registered (AQHA & APHA) weanling colts for $150 to $250, one was only $65 which was sorely in need of care and it turned out nicely. Fillies might bring a bit more; everyone is looking for more mares to breed, (like we need more)!

Breeding this time of year would depend on where you live. In the south, I would say not past July 1. Between the flies, monster horseflies, and heat, it can be miserable for a foal and mare. And in the last couple of years, we've had summer drought here in Texas. No grass left. The spring was great.

I admit that I have my mare at the breeder right now on lease to a friend who was recently diagnosed with ALS. This may be her last foal to enjoy, so I agreed to try a late foal. The stud fee had already been paid, but they lost the mare they had intended to breed to this stallion. But my mare is 19 and hasn't had a foal in 4 years. That time took 2 breedings to get her pregnant. The first try this time didn't take so we are short-cycling this week for a last chance breeding.

Before you breed, decide what your intention is for this foal. What will you breed for? Will you keep the foal and train it? Or will you sell it? Around here, foals sell well as 4H colt projects, but you need to get the word out that you have a colt available as early as possible. Colts sell better than fillies here.

If you decide to breed her, start earlier in the spring, in case there needs to be multiple breedings to settle her. Some breeders will allow you to carry over to the next year if the mare doesn't take and it gets late in the season. Make sure you get it in writing.

I agree with fancifowl. You can get some great deals on weanlings in the fall. Especially breeding stock paints. Even show babies can go as cheap as $1000. For non-show quality, they can go for $400-500. Your stud fee will likely be more than that. Check around with breeders in your area, or check with the ag extension agent that handles the 4H horse projects. They know sources for great deals on foals.

I had a mare who I loved very much,she loved me. I got her in 1970 at 14 months as a totaly unhandled horse. I trained her and she taught me. She died in 1999, but she left me her son, Ralph who is 29 now(seems like yesterday). Breeding her and keeping her son is the best thing I have ever done. He was born in my arms, everything that happened to him I know. He is the perfect horse, I did 50 mile races with him 3 day eventing(no small task for a 15h Arab) I used him one summer for leading trail rides. I gave riding lessons on him, now we just trail ride and camp with friends.

That is such a sweet story! Just what I hope to acheive. If we breed we will probably do so next year. Thanks everyone!