Hi,
Is your daughter's email address in your webmail or offline client's address book/contact list? That should do it. There should be an icon or other sort of link to allow you to quickly add her address to your address book. If not, you can do it manually.
OTOH, if your daughter is sending to you from
different email addresses (say, one from work, one from home), it could be causing the difference.
Or maybe the contents (one email containing lots of links or online photos gets treated as spam while a simple text message gets through).
If adding her address to your contact list doesn't solve the problem, see if there's anything the ones treated as spam have in common.