What are you planning on doing with the foal? If you are keeping it and the mare for a long time, then I would say breed if that is what you want.
If you are planning on selling then DO NOT Breed at this time.... I worked at an arabian farm that sells really high quality show horses ranging in price from $2000- $75000. They haven't sold a single horse in at least 9 months. They have about 30 head with 6 foals on the way. These are top quality horses and they can't sell any of them. Even the horses with training.
I know how tough it is to decide not to breed. I would really like to breed my mare who I've had for the last 10 years but there are just so many horses that are in need of homes right now. At the moment, I am trying to find homes for 5 TB's that are going to be put down (nothing wrong with them just not trained), rescue a weanling from an abusive situation, and re-home my last rescue.