The story of my life.
From my experience, unless one or both of you are super emphatic and guilty about it, not much can be done; I'd say it's more or less normal in that period of life. What I can confirm, tho, is that once she graduates, things might change again. Actually, it's a given. It happened in case of my sister. We really grew apart during her university days, but once she graduated and came back with her 'boyfriend' (), things changed drastically. I'd say it's not exactly the same as it used to be, but nevertheless, we restored the bonds that once tied us together. I'm actually amazed it came so naturally, as if nothing happend to the point, it left me confused for quite a bit as how to react; luckily, her boyfriend is a super cool guy and literally became a bandaid in our relationship.
I'd say, don't fret about it that much. Just be yourself and keep reminding your sis, you're still there for her. She's propably before the period, where an adult person actually comes to understand, how important and precious family bonds are.