My very best friend is now in Atlanta, we have gone months without talking. We are both busy, with different schedules. it just changes. I had not physically seen her in about 12 years and then my daughter and I were in Atlanta a few years back.. we olny visited for 2 hours, but even my daughter commented, it was like we see each other every week.. We were still really close.
Do give her a chance to call you. You could even send her a note and just say, you can tell she is super busy, so you are going to let her call you next. Let her know this is not a test or any pressure, you just want to make sure you are not bothering her. and then do it.. Move on..
I have lots of best friends from all sorts of situations.. We may not see or speak with each other for really long times, but when we do, it is as though we just got off the phone that morning..