I have a friend who owns an afflicted HERDA paint mare. Don't think for a second that the AQHA or APHA are doing anything to protect the horses and owners in their assoiations by even admitting that HERDA is a problem in their gene pool. They do not require any testing of breeding stock and if you do test, your results will not be included on the papers (unlike HYPP that mandate it for AQHA registration). They appear to more intested in protecting the legacy of certain stallions than protecting the future generations.
The good news is your mare isn't afflicted. If she were, she most likely wouldn't be alive or she would have disfiguring scaring over her back that there would be no question as to her status. Doc O'Lena is one of the very few named known carriers so since she is double bred DO, she very likely could be a carrier. That would be important if she were ever bred. If she is a carrier, if you choose a non carrier, she cannot produce an afflicted foal but will produce another carrier 50% of the time. There is also another potential carrier, Bueno Chex, on the top side. UC Davis does the hair test for $40.