Why would a 24 year old girl hangout with a 40 year old couple?

We known this girl for the pass 6 years and shes willing go to movies or dinner with us. She has a bit busy schedule but she will make time to hang out and go places with us .. I've liked her for quite some time but she doesn't know that tho. When she had a boyfriend we didn't hear from her much but now she's willing to hang out. I wish that I hang out with her alone and go to dinner alone or movies but I'm just nervous to ask. My chick and her text from time to time but I would like to have her number to.last time we hung out said asked if she can keep the tickets. Is there some kind of explanation why she is hangout with us? How can I let her know I'm into her. I sorta of spoil her when we're all out. Any segustions?