It looks like the confusion over Hattie being Mary's Mother was the way the Census was originally written down. There were house and family numbers written next to Hattie's name, making it appear she was in the Angel household. The numbers were then crossed out, but when the census was transcribed at sites like Family Search, the transcriber left her as head of household with the Angel's, . I am thinking the house and family numbers should have gone next to Charley Angel, but were not. There is nothing we can do about the original census records, but at least at Ancestry, a comment can be put to go with the census.
That's why we are supposed to analyze what we find - it would be possible for Mary Angel's Mom to be born in the US and to go to Poland with a husband, and give birth, but not likely.