Will a 2nd computer in iCloud cause a sync issue?

Thanks in advance for any help that you can give me.

My friend is in town from another state. She brought all of her devices and 1 of her 2 computers with her. Her computer files and devices were completely disorganized and not synchronized properly for iCloud and iTunes. I helped clean up her address book, calendar, etc and I also helped get her Macbook Air, iPad mini, 2 iphones, and an iPod Touch in perfect sync with each other via iCloud and iTunes. Everything now matches on each of those devices and her Macbook Air. Her iCloud and her iTunes account on each "just work" together as they say and are now in perfect sync. Her Apple "ecosystem" now works like a charm!

Our concern is when she gets back home and opens her 2nd computer (a Macbook Pro), which is the only computer/device she didn't bring with her on her trip to see me. Her Macbook Pro back home is still a mess with a disorganized calendar, address book, mail, etc. and she is also signed into her iCloud account and her iTunes account on this Macbook Pro. The worry is that when she opens her Macbook Pro back home it is going to undo all of the work we did and update/sync its messy address book, calendar, mail, etc to all of her devices and the Macbook Air that we so carefully cleaned up. First, is that what will happen when she opens her 2nd computer back home? Second, if so, what can I tell her to do when she gets home to the Macbook Pro to prevent the mess on that computer infecting her now perfect Apple ecosystem?