breeding older mare

Question
I live in nth west Queensland Australia I have a 20yo arab mare who appears to be in excellent health no one believes she is 20.  She had a foal at 14 and had normal cycles when I got her at 17. We mated her (to our vet's stallion) that year; were told she was in foal, she looked in foal, but come due date and nothing happened. vet said after examining her, that the foal had died at 5mths and had mummified, over the next 2 weeks she gave the mare 2 injections to induce the fetus but we saw no evidence of anything being expelled, but the vet said she was now empty.  The mare didn't appear to have a heat cycle after that until she was put in a paddock with a strange gelding a month ago then she backed up, did little pees, blinked her vulva and had her tail to the side. all the signs of heat she used to show.I must say though she is not doing any of this when she is with her regular paddock buddies both geldings.  Is this mare too old for me to try again for a foal?  Will she loose it again (if she really was pregnant)  

Answer
JUST MY PERSONAL OPINION, BUT I DO NOT LIKE BREEDING 20 YR OLD MARES. THEY CAN GET IN FOAL, BUT THE FOAL IN NOT NURTURED IN THE MARE AS WELL AT THAT AGE AND YOU USUALLY
YOU GET A SMALL CROOKED FOAL. THERE ARE EXCEPTIONS OF COURSE, BUT I DO NOT LIKE THE ODDS