Yes or no

So my boyfriends mom walked out on his family when he was like 4. She lives out of state but keeps contact through Facebook. I think shes awesome and she loves her grandchildren. Ive never met her in person though.. Anyways, his dad is engaged to a women hes been with since before my son was born or i was even pregnant with him. Hell be 2 in October. Shes pretty cool too but shes like the perfect.. The perfect spouse, mom, everything.. We consider her a grandma to our kids but should i consider her my MIL? We do plan to marry.