Good Morning and welcome. I am Dr. Loretta, a licensed veterinarian and I am happy to answer your question.
Thank you so much for so much detail...I feel like I already know you...and Adrianna.
As you are aware, cats have a very difficult time with change especially as they age. This time , after losing Lucianna, it is even more tough on her. Cats can change but it does take time and patience which I am sure you are willing to do....my fear, though, for you is Adrianna's age. This may make thing even more difficult due to the possibility of dementia and organ compromises.
The first thing you should do is to purchase Feliway and Rescue Remedy at the pet store, These are holistic medications aimed at decreasing anxiety which is why Adrianna feels so afraid and distant. Use this as a diffuser and during this time allow her to investigate your girlfriend...never force her into anything. if she does show up where the 2 of you are, talk to her in a low calming voice which will help her feel safe and help her over her fears.
I would recommend that you have your vet examine Adrianna and run a full blood panel to be sure that some of her issues are not related to pain from arthritis or other metabolic issues. If the Feliway is not enough, they will have a medication called Clomicalm that will decrease her anxiety even more and help her to accept others.
Lastly, it may help to consult a veterinary behaviorist. You can do this as a phone consult and they will have other tips to help Adrianna more comfortable in her environment. You can find one at this LINK. This is not expensive.
Does that make sense to you?
Please let me know if you have ANY other questions. My goal is to give you 100% satisfaction and if you are not yet satisfied, please Reply so I can clarify for you
Sincerely, XXXXX XXXXX