Was she so bad to her? She was one of the leading anti-Katia figures at the Court, leading to strain between her husband and his father. I never read in any of the bios of MF that she had a bad relationship with her mother-in-law.
Actually Maria F. was not bad to Maria A. But at the same time they did not get along very well, MF respected MA but the two were not close. In a recent Russian bio on MF there are some lines on this fact.