I have been busy caring for my 90yo father who has dementia and just now logged back into this site and saw your response - thank you!
It’s likely that the mineral rights were inherited from her father’s family, who settled in Pecos County in the late 1800’s. Her grandfather and father were both attorney’s who accepted fractional mineral interests as payment for legal services. We have record of a dozen or so properties, but this one was not in the paperwork she received when her father passed. But this new discovery does make me want to do some in-depth research to find out what else there might be. Thanks again for taking the time to respond!