Befriend Her Future In-laws
If an engagement is in the works or has already happened, you'll want to spend some time getting to know your daughter's future in-laws. It's safe to say that when two people unite in marriage, two families are also united, and it will be important for you to get along well with your daughter's new family. Establish a good relationship so you can amicably divvy up holidays and so your kids maintain a connection to their families as they're building a new one.
Invite the future in-laws over for dinner, or take your daughter's future mother-in-law to see the ceremony and reception venues. Also, don't be afraid to spend time with them on your own without your daughter and her fiancé. After all, they'll become your family, too!