Bonding problem

Hi
I have a 6 year old Netherland dwarf female who lost her mate a couple of months ago. I’m trying to bond her with a 2 and a half year old Netherland dwarf male.

Both are neutered. I have a small hutch inside a large shed with run attached. I usually just leave the hutch open. I put new male rabbit in the hutch so they could get used to each other’s smell.

I’ve brought girl rabbit inside for a few hours each day so that boy rabbit can have a run round. After 5 days I tried putting them in the bath as suggested neutral area and gave them about 5 minutes together. They were okay yesterday but today the girl stated trying to nip the boy on the neck - I separated them and am now scared of putting them together in case she hurts him. Any advice please?