The FU isn’t with you, it’s with your manager. She clearly was able to get ahold of you so got the message. She should have said “we have a policy, I will let this one go but you need to know for next time the proper procedure” it’s also her fault you didn’t have her number.

I say this as a manager with a sick policy. I always give my employees one chance and remind them of what the expectations are. After that it’s on them but the first time is always an exception.