I'm currently bfing my 13 week old son and will continue to until he's on to cows milk, for cost reasons.
I personally don't think I'll continue beyond one as I find the idea icky, I find past 6months a weird (for myself, not anyone else, each to their own) but we can't really afford formula and bfing is going very well. I might get to one year and change my mind, I'm fully prepared for that.
Regardless of her personal feelings you MIL is very unreasonable to say anything negative toward you. Your baby, your choice.
My MIL is big advocate of bfing (especially in public!). My mother on the other hand will tout out 'breast is best' then ask when I'm stopping, she didn't bf any of her 5 children, and both my grans are similar (why would you want to, I couldn't be doing with that etc etc) my grandfather on the other hand is a mega advocate- it's cheap, it's convenient, no bottles at night, what's not to love (he says).
Regardless of what my family's views are, my views are the most important and I just smile and nod, and put DS on the Boob.