Texts from phone number coming through as SMS, but iMessage turned on. Texts only come through their iCloud email?

My family recently upgraded to the iphone 16. For some reason, my phone is not recognizing my mom’s number as an iMessage number. However, she says my dad can text her number and it goes through as an iMessage. When she texts me now, I only get it through her iCloud email. I’ve done everything to reset and try it again. Why is this happening?