If anybody ever tells you that all your parental responsibilities end when your children turn 18 has either never had children or never been a real parent. They may grow up and move out, but the bonds that develop between loving parent and child are never severed. Strained, perhaps, but never truly severed. Being a parent grows ever more difficult as your children grow older simply because they do become adults, with their own independent wills, dreams, and ambitions totally apart from yours. The best you can do is offer advice when asked, both sides knowing that the advice offered is from a different generational perspective, and the older generation realizing the younger generation may decide not to take that advice or modify it to suit the current situation. You can be there to help them the best you can when they need it. But if they don't ask for advice or help, then you have to stay out of their way, realizing that you don't have a complete awareness of their situation.
I've come to realize that the best way to be a parent to an adult child is to give of my time and go to them when it's convenient for them rather than demand they come to me. When young adults are starting out they're incredibly busy and their money is stretched rather thin. That means they have neither the time nor the means to take numerous junkets to visit the parents as often as the parent (and the child) would like. Realizing this we've decided to go up and visit the girls on a semi-regular basis, when everybody's schedules can mesh. It really works out best, as we get to see each other, and we get out of the house and travel.
I've also come to realize that the younger daughter is reaching out to mom about adult woman issues. That's not to say I'm no longer loved nor appreciated; I am. But my daughter has reached another point in her life where she needs mom again, especially mom's insights. It's a good thing mom was an English professor for nearly 25 years. During that entire time she taught college-age students which, coupled with her unique innate abilities to understand young adults, is now helping both girls navigate some of the rougher patches in this part of their lives. If it sounds like counseling, it is only in the broadest sense. What is happening now is far more sophisticated and nuanced, as this is between two human beings who have grown up and grown older with one another. And I'm glad my wife is around, because I would be helpless in these situations.