After an update my Granddaughter cannot receive texts from me but gets all my other texts

Welcome to the Apple Support Communities!

I understand your granddaughter is not receiving the messages you send to her iPad since you updated your iPhone 6s. What other device is she using that is receiving all your other texts?
The first thing I would suggest is to have your granddaughter update the iOS on her devices as well. Then each of you can restart your devices and try again.
If that does not resolve the issue, here are some additional troubleshooting steps you can try:
If you can‘t send or receive messages on your iPhone, iPad, or iPod touch
Take care.

Hi

This is because you have the same apple I'd they are not made to share Everyone needs there own apple I'd if your granddaughter is 13 or over she can have her own apple I'd

Cheers

Brian 🇬-1F1E7;