When my grandmother died, I received her recipes. I spent 6 months (while I was home with my newborn) typing them all up and making recipe books for everyone in the family for Christmas. Out of the estate, my parents paid me $250 for the work (unrequested).
I took the $250.00 and bought a lovely cameo necklace of a mom with a baby. I plan to hand it down to my daughter if/when she becomes a mom. Something along those lines would honor your MIL and also have something "tangible."