Frederik not so much demanded Catherine to come and see him before she was off to Russia,it was usance for german
bred noble brides to say farewell to their Monarch,as he was to give permission as well for a marriage ins ausland,
upon leaving the country to get married abroad.
So,you can't derive anything from that visit.
I think the best books,and the person with absolutely the best and most intimite knowledge on Catherine the Great
is Isabel de Mandariaga,author.
She,nor any historical,or histerical if you wish,paper/document referres to Fred fathering her.He didn't father around
that much,his interests "lay" more with the same sex thing,not a bad choice either.And it keeps one from false accusations.