Our last name is Murray, so I think it sounds okay with it.
It's the history of the name that's really meaningful to me: My grandmother was taken from Poland during the war, and when she came to Ireland with my grandfather she changed her name and was always known as Marianne or Marie. It's always felt very sad to me that she left that identity behind along with the rest of her family, and her own language (which she's never spoken again).
I'm very close to her and when I was little shed used to tell me about what sounds like a delightful childhood... I love the idea of there being another happy little girl carrying her name into a happier life!!
On further consideration I think it is rather nice, especially with your surname. I think you should go with it unless it would actually make your Grandma sad to do so. It is lovely to have a family name and story to pass on.
You will have to get used to her being Maareeeshaaa Mooreee some of the time though!
I think you should use it only if you really like it on its own, apart from the history. It sounds like your grandma put the history behind her, e.g. not speaking the language again (not even with your GF - assuming he was Polish too?).
My Grandfather was Irish - he was in the Army and was part of the regiment that went into the camp to liberate prisoners.
My grandmother did put it behind her in a sense - but only because it was too painful for her to ever talk about. She didn't speak much English and suffered a lot of abuse when she first came to this country.
She never knew another Polish person here, and never knew if her own family had survived the war or not.
Sadly she has Alzheimers now and won't be aware that her name is being passed on. Her life has really been a very sad story but I feel pretty strongly about passing on her name because she had the kindest heart (I'm sure most people think that about their Granny's but I'm convinced it's true of mine!!)
And I think maybe it sounds better said with an Irish accent Sock!
TBH I feel like changing it would dis-honour her in a way... she called herself Marianne or Marie to fit in when she got over here and it always seemed very symbolic to me that she felt like she had to change her name... it was like in a way she had to leave behind the person she was. The stories she told me of her childhood when she was Marisha were of a happy childhood as part of a big family, in a beautiful area and as Marianna/Marie she lived a very lonely unhappy life in an alien country. I do love hearing everyones opinion though