You can search for unclaimed mineral funds in the state of death and also on the MOEA Search. Use the state treasurer’s site, not any of those that state they will “help” you (they charge). You should also check Delaware, just in case because many companies have their domicile there.
If she did not have a will, then you will have to settle the estate in the state of her residence under their “Intestate” law. Then once it is settled in the primary state, you need to file a “foreign” probate in Oklahoma using an attorney licensed in OK.
If you wish to post the section, township and range, one of us will look up the wells that have been drilled on that section and then you will have a better idea of what past production you have missed.