Late to the game!

I am the mom of 20 year old twin girls. Until recently, they were inseparable -- they went to the same school, were in many of the same classes, and even had the same friends. Even though my husband and I encouraged them to do otherwise, they chose to attend the same college and decided to room together. Both girls are very shy, so they have always relied on each other. Now (finally) one of my daughters is starting to blossom! She is joining clubs, meeting new people, and dating. This has been very hard on my other daughter, who still relies on her twin for companionship and social support. It's very hard to watch her struggle.

If there are other moms of young adult twins out there, I would love to get your perspective. How can I help my "dependent" twin adjust to the separation?