The other woman / Jane Green.

Enhanced descriptions from Syndetics:

From the New York Times bestselling author of Falling and Sister Stardust comes a novel about marrying your dream man--and his mother.

When Ellie meets Dan, she thinks she's found the perfect man, complete with a loving, close-knit family. Having lost her own mother young, Ellie looks forward to gaining the mother she never had. But first signs of trouble appear when their intimate civil wedding ceremony is transformed into a full-fledged black-tie affair, and Ellie starts to wonder if Dan's boundary-hating mother, Linda, might be a little too involved.

As troubles between them mount, Ellie turns to her friends--glamorous Lisa and wonderful frazzled Trish--to help her recapture the independence she once had, and the man she still loves. But having her own child makes Ellie realize that the unconditional, sometimes overwhelming love of a mother is something that can't--and shouldn't--be ignored...