The problem is that she is also part of a shared mailbox
Sorry but I cannot understand the situation.
Do you mean this user mailbox has given full access and send as permissions to other users so others can use this user mailbox as a shared mailbox? (In other words, it is one mailbox with a single email address or two different email addresses)
If this is the case, I am afraid it is not possible, as rules won't be able to tell which emails are sent to the user mailbox and which emails are sent to the shared mailbox.
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