Why can't I send iMessage to a family member's phone number instead of their email address?

Two iPhone 16 running iOS 18.3.2. When I send an iMessage to my 14yo (who is set up as a family member) it will only show her email address as an option. I cannot get it to send an iMessage to her phone number even if I type it in - it reverts to the email.

On her phone her iMessage is set to only send from her phone number. I have tried having her only receive at her phone number and it doesn't change anything with how I can send to her. Even when email is not checked, messages from me still go there via iMessage.

Other family members do not have this problem - when they type in her name her phone number comes up, and their phone will send an iMessage to her phone number. I am the family organizer if that makes any difference.

In addition to following the usual steps to make sure that she can receive iMessage from her phone/email, I have tried:

• deleting the contact card for her from my phone
• turning her iMessage off, doing a network reset, and turning iMessage back on

If I remove her email from the contact card (but leave the phone number) it changes her appearance in Find My to the email that I had deleted from the contact card. Then I get endlessly lost in sharing settings to make sure that I can still see her location.

Sometimes when I am messing around with settings and she messages me, the banner preview says it is coming FROM her phone number and TO both me and the name I have on the contact card for her...as if it was a group chat somehow.

I can't rely on being able to message her via her email address because we live in an area with frequent dead zones - I need it to be able to send as SMS to her phone number at times. Screaming in to the void hasn't helped so I am hoping someone here can.

[Re-Titled by Moderator]