[Anypeny]

It is a great injustice that one rush to devorce. Your reason doesn't necessitate devorce. Even if one consideres niqab to be wajib, not observing it may make her sinful but not a bad muslimah.
She may feel it is not important for her to wear niqab! She is not violating any of your rights!! Instead work on how to be caring husband. In it there is more reward then ruining fellow muslimahs life.

but how can i view someone else as sinful for not wearing the niqab? Surely if there is ikhtilaaf then I cant view people who dont follow my opinion as sinful?