C.J.
Just curious. Has she shared that this moving on is frustrating and confusing for her? Has she told you that she misses this friend?
If not, don't jump to conclusions. She may be happy with the change.
If yes, continue to encourage her.
Point being, yes. I went through this. I had two besties from the time I was five years old through sophomore year. Once in High school we found different cliques. And when I stopped playing basketball our friendship was not as tight, but we were still pals, still hung out and still had a great time. My mom was sooo worried that I was changing friends, falling into the wrong crowed (was not, btw) or that we all had a fight (we didn't). It is normal and all her worrying was frustrating and smothering and unnecessary. I didn't talk to her because there was nothing to talk about.
Give your daughter her space to feel it out. If she comes to you for advise, give it. If not, she is probably doing just fine:)
Thanks for your SWH. Sounds like she does need some extra support. Good job, mom!:)