First of all, reining training makes any horse s better broke horse, no matter what their ultimate job will be. So, reining training is not wasted unless you put many months more in training than you will get done in some other discipline or use.
But, I have another question: At what level would you like to rein? Are you thinking about NRHA -- even at the 'Rookie Reining' level?
Are you thinking about AQHA or possibly Open or Foundationbred shows?
She has no modern reining, cutting or Cowhorse breeding. What performance breeding she has is very old, at best. It is very difficult to have any horse train or show at a very high level that is just old Foundation breeding that does not contain modern cutting, cowhorse or reining breeding. They just do not have the extreme athleticism, quickness and the kind of mind that can withstand the pressure it takes to 'finish' a reiner.
So, if it were me, I would limit how much training or money I put into reining training when the horse is not bred to be a reiner or at least a cutter or cowhorse. The discipline has gotten so precise and the competition has gotten so tough, that you do not even see many new horses now that cross over from cutting and cowhorse to reining.