Since he has accused her of lying about who paid tuition saying he has the bank statements to prove it, he needs to produce them.
Or maybe he was lying or grossly exaggerating about his contribution.
Then being caught needing to produce the bank statements threw her out her letter to him instead to change the conversation.
Which it did quite handily.
I want to see proof of his statement that she lied about the tuition and he paid every penny of her tuition.
That may come up in court, who knows? As for Markle, Sr. making them public now, he might want to be careful about that. Whichever newspaper chooses to run that story will have to deal with a lawsuit from MM.
Bottom line: why would her father lie about such a thing? What would be his motive?