OP explained that the counselor wanted it to review information on her own time. Seems like a nice and helpful counselor to me, and if I were a counselor I can see wanting to review information late at night when I can find a quiet period of time, not in the school office with kids and other adults constantly asking for help.
My first gut reaction to the counselor’s request was NO WAY. Good intentions or not, it’s the student’s responsibility to fill out the app and proof it. Besides, I wouldn’t want the counselor having access to my kid’s app, just in case she unintentionally hits a button by accident. Just not a good idea in general with something so important.
There is a way to keep everyone happy:
https://appsupport.commonapp.org/ics/support/KBAnswer.asp?questionID=7&hitOffset=11&docID=2660
If the school counselor insists, honor the request and share a temporary password. Once you created a basic password, memorize it but prepare a list of alternative ones. If your password happens to be ABCStudent101, just create a ABCHS101 and share that account. After the meeting, revert to the old one, and rinse and repeat for every meeting or request.
With a private counselor, you should have full trust and allow the counselor to check on the more arcane parts of the applications. In every case I helped someone, I found incomplete or inconsistent information. It really helps to have different pairs of eyes on those applications as one person tends to NOT see a missing line.
Even with that explanation, I say NO. And sorry, it doesn’t even seem kosher to me for the counselor to ask. I’d have a hard time trusting anyone who asked my login info for anything.
It just rankles me, and should bother everyone, that students are warned from early childhood NEVER to share passwords, even with a good friend. A counselor should be sensitive to this fact, and not be so cavalier in requesting the information.