It is probably from looking at the death records of their children. I have not seen her maiden name spelled the same way on any records that I have found(online). I've been trying to find clues of when they immigrated and with what family if any. I haven't had any luck.
Joseph Messbarger + Anastasia Hammond> Thomas Jacob Messbarger + Anna Mcgraw> Adelaide Messbarger + Arthur Shawver (Adelaide Messbarger died a few weeks before Mary Louise Messbarger Denton)