IMO that is just fine for breeding... Many people will show their mares and then breed after they have reached their "prime" for showing. We had a mare in her early 20s that foaled out (with vets approval) and didnt have any problems and she passed away when she was 32.
--Wow-- that's amazing, your very lucky, you must have been proud :)
Will she be bred to a registered stud? I remember seeing a couple prospects for her that werent and just wondering the reasoning behind that. You could always give an unwanted animal a home and buy a baby haffie. JMO