I believe it is a bone knife, used to fold a signature of pages for book binding. When I took a book-making class in North Carolina, that was the type of knife we used.

My Great Grandmother and both of my Grandmothers had them also - letter openers. Maybe your friends grandmother used hers when pulling the thread out from under the foot after re-threading the machine.

Hi I am no expert but it looks like part of ivory made for an envelop cutter-- quilt for fun Grandma G

My MIL gave me one so many years ago. I still have it. It's a letter opener. Use the straight edge.

That definitely looks like a letter opener. Not sure why it would be in with the sewing stuff, but might have been used to cut folded tracing paper to the desired width. I know we used strips a couple inches wide for most of the marking we did with the tracing wheel and tracing paper.

I'll bet she had it in her sewing stuff to push the corners out after sewing. I'd use it for that for sure...

Letter opener for sure...but those are almost always not bone. Stick a hot pin in it and see what happens. If it's plastic, it will melt.

Interesting comments from everyone... Any antiques shops near where you live? Maybe someone would be sewing items savy and be able to answer.. Post whatever you find out.... Its an interestng item, and I love history about sewing item.