Long ago when we were first married, we had a gray maine coon type cat. She was over a year old, when we introduced the second as a kitten. They would play really roughly....I thought it was horrible. I mentioned to the vet, and he said cats do this.
That they have thick skin and what hurts us does not hurt them.

But given that Daisy is soooo little, still, I'd be careful too.
I don't think she will try to nurse off him now either! She has probably learned that!. I'd stick around when they are together for a little while yet, until you see some improvement.
She is so small you could step on her, or she could get injured in the kitchen, etc. Doors... always a risk with doors.
I'd get down on the floor with them, if you can now and then. Showing them YOU are boss, and watching. This always worked for me.