Interesting! To me, this indicates that perhaps she left it not because of anything to do with Catholics but because it had simply become such a restrictive splinter group that as she moved out into the big world she realized that it could never be, in a sense, the "true Church," and that anything that exclusionary was essentially a sect in the worst sense of the word (very akin to cult).
It sounds as if they didn't even get along with other Protestants or even other Lutherans, not to mention Catholics.
Makes family gatherings rather strained at times!