Re-bonding with a cat

Hi everyone. I've been meaning to write here for a while. I've had my cat Luna for 2 years. She was a very fun and affectionate kitten. Unfortunately 4 months after getting her, i had to go away for 3 months on a trip. She stayed with my dad and they became super close, and she was VERY affectionate with him during that time period. Fast forward a few months, i come back, shes not as close to me as she was before (understandably), but still very playful and cuddly at times. She would be especially cuddly when alone with me. She then had to be operated on, she had a bad case of pyometra, so they had to remove her uterus and ovaries. Ever since then she has been growing more and more distant. She rejects our touch. She'd meow for minutes on end, and if i got up to see what she wanted, she'd become aggressive. She seemed very lonely and like she wanted a friend to play with and keep her company when im away at work. So after much deliberation, we decided to adopt another cat, a 2 month old kitten, Mia. Luna was very reluctant and aggressive towards Mia at first, but has come to accept her. Luna is now 2.5yo and Mia is 6 months old. Altho it seems Luna accepted Mia, Mia is very dominant and "disrespectful" towards her. She always steals Luna's food and treats, and "invades" her safe spots. For example, if i want to give Luna a treat, i have to lock Mia outside the room. Mia will start meowing loudly which leads Luna to not even eat her favorite treat. She simply refuses. Its like she's deeply emotional, and can feel every energy shift. Everytime i try to approach Luna she is aggressive and shows signs of not wanting to be touched. She only enjoys being brushed (very rarely, and always in the bathroom carpet) and if i go 1cm off she'll bite me. She's, in general, very aggressive and not affectionate towards me. How can i show Luna how much i love her while not ignoring/paying less attention to Mia? I just want to have my baby back. I miss her so much. If you have any advice or lived through something similar, please leave a comment or dm me. Thanks for reading!