You don'[t have enough information to be able to understand this situation.

You say that "something" happened. You don't know what and nobody is telling you.

Clearly that something was a big deal, big enough to cause an estrangement.

Without knowing what that something was, there's so way you can effectively mediate this.

It could be that if you knew what had happened, you wouldn't be criticizing your granddaughter for "shutting down behind an angry wall."

You might be applauding her for protecting herself.