Ragdoll kittens & cats in South Dakota

Millie is a 3yr old cat not neutered but we can no longer keep her due to the cost of food and medical bills, plus our boy black seems to not want her around anymore he's been attacking her from time to time she will not be doing anything and he goes after her, she is great with our 6yr old and 13yr old is her favorite human but when my husband or I try to pet her or go near her she runs from us and hides she has been like this since a kitten at one point we gave her back to the people who gave us her because she was acting so strange and timid and when they told us they worked with her and she had become more affectionate with adults we decided to bring her back home she instantly went to the 16yr old and purred and day later she was acting as if she was afraid of everyone but the kids anyone can come visit and she will hide the entire time and since she has started to get picked on by the black cat and she's mean to the young one over food she's started peeing in corners of our home