Interesting thread! I only ever had a mother-in-law ... but back in the late '60s, it wasn't "quite the done thing" to use her Christian name. Nor, on the other hand, did I ever get around to calling her "Mum". However, once the kids came along, I felt able to address/refer to her as "Granny".

Times have changed, of course ... and nowadays, I'M simply known as "Arthur" by both my son-in-law and future daughter in law.

But yes, Alona, it's really nice that Luke's mum likes YOU to call her "Mother".