If D3 wants to call or send something to Daddy, I’d just do it. Especially one way communication like emails, texts, letters, and such; H can open, read, and respond as he will. Phone calls and line video chats do take a bit of scheduling.
It is not your job to maintain or create the relationship between H and his daughter. It is your job not to destroy it.
Obviously, D3 is three. She is going to need some help in the logistics of long distance communicating. She is also going to need guidance in her growth. You are going to be involved when she asks why Dad did or said certain things. Just like if he was here, D3 would still have questions. Remember your job. Facilitate when D3 needs help. Validate and explain when D3 has concerns.
I wouldn’t send anything about a communication schedule or strategy. Let H see and feel and suggest something.
DnJ
Feelings are fleeting. Be better, not bitter. Love the person, forgive the sin.