Focus on your new family now. Your husband to be deserves your loyalty even over your mother. Your baby deserves your loyalty even over your fiance (until he marries you, at least). Both of them are higher on your priority list than your mother, now that you have them. Grow past the "my mother is the only one I have" mindset or you will have trouble being a good wife.
My dad was absolutely furious when I told him I was pregnant. Now ever since he seen her he's in love with her. Don't fret too much she'll come around(:
She not the only one you have any more. You have you fiance and your beautiful baby waiting to meet you. (: let her have her space shell come around. If your happy she has no reason not to be.