I like (and also depends on flow to your last name):
Mary Elizabeth Josephine* (I like this order once I imagine a last name, other way to me sounds like two separate names)
Mary Christina Elizabeth*
Mary Elizabeth Josephina (smoosh of her two names)*
Or you could go with something further afield:
Mary Elizabeth Josie-Christine
Mary Josie Elizabeth
Mary Elizabeth Chrissy
Mary Elizabeth Christine (love this flow)*
*All faves! Maybe Mary Christina Elizabeth is the top-top if had to choose. But there are a number of delightful options to honour your grandmother…