Maiden names not always included in obits, unless a surviving brother is listed.And, besides year of death, you will need at least month, also, to look for an obit.
Your mother's death certificate should show the names of her parents, including her mother's maiden name.Now, accuracy only as good as the knowledge of the informant, and I see they have her listed on TX Dth Idx as Dorothy P. Wehrung. [By the way, the index also shows your mother's death date as Mar 9, 1978.I checked your message history for any additional info, and see you have the 10th.]
Your mother would have filled out her own application for her Soc Sec card, and that should show the names of her parents, which she would have known. Good luck, and happy hunting. (^_^)