Thank you for the additional information. Oklahoma is among a handful of states that still recognize non-ceremonial marriages, also referred to as “common-law marriages.”
If your father and this woman both held themselves out to the each other and to the public as a married couple and lived together it is possible that she could establish a common law marriage and have status as a surviving spouse.
It would be her burden to prove that the elements of a common law marriage were all met. As an interested party you can open an estate in probate
. If there is a will it will need to be produced by whomever is holding it. The lawyer can probably help you with that.
If there is no will then you will be entitled to a share in a portion of the estate along with the other children, if any.
Since it appears you do not live in the same county as your late father, you will want to retain local counsel. The lawyer you spoke with may be able to help with that, as well, even though he may have a conflict prohibiting his representing you himself.
I hope this is helpful. If you have any follow up questions feel free to post them. It is never a problem.