I had/have exactly the same problem. My mum never breastfed and has certain ideas about how things should be done which she seems to think must be right as she's "done it all before". Problem is, a lot of it actually isn't how things are done nowadays. She's also into buying all the latest gadgets and loads of stuff we don't need whereas we are completely the opposite!
It's basically a power-shift - you are becoming the Mum, she is becoming the Grandma. Once that baby is born, you are the one that has ultimate say over how things are done and she's not used to that. Just as you will need to get used to a different role, she does too.
My mum's wanted to be highly involved all along - first of all offering to come and stay for 2 weeks straight after the birth, then being at the birth itself. While I'm going to be glad of the support, we don't need her to actually live with us for 2 solid weeks - she only lives half an hour away! I want time to recuperate and time alone with just baby and DP. I told her I only wanted DP at the birth and she was a bit offended.
I think it's a case of setting boundaries and letting her know that the way you have decided to do things is the way it's going to be. Perhaps letting her know how she can help in ways that will support you most and also letting her know areas where her input is not needed (in my case, feeding).
You want her on side and helping but you don't want her running roughshod over you - it's a tricky balance. I actually don't tell my mum that much, it's quite "need to know". I've also enlisted my brother to be Kofi Annan and I've told all family that DP decides who visits when and his word is final and law.
Good luck, it's a horrible feeling I know.