Needing Advice!!! Unhappy/Memory Loss etc

Alright so this is very hard and have been dealing with this for a while now but I honestly don't know where to go from here or what to do. Can someone please help me and give me some advice? My mom has been cancer free for 3 years now which is awesome. Unfortunately she got a really bad case of shingles as well and she has tried nerve block and all kinds of different medication. We have noticed that her memory is not that great and will forget things that we have told her both long term and short term and I can tell that she gets really frustrated and angry towards whoever is telling her that she forgot something or that she didn't tell us something that she had thought she told us. It truly seems that she is VERY unhappy. I can understand where she gets frustrated but she won't let us help. She won't share what medications she is taking and she won't let us come to doctors appointment etc. This has caused a very bad situation...she thinks that everyone is against her and trying to make her think that she is crazy. There is a big disconnection between her and my dad and always fighting and arguing over things that dont make sense or over him trying to help her. Any time my husband and I go over there if my dad says one thing she gets mad and rolls her eyes or walks off shaking her head and I am not really sure why? I know there might be things going on that I don't know about and its their marriage but as of last night my dad packed his things and left. Last year I talked to them both and told them that needed to go to a counselor together to talk about things because I couldn't be their mediator. She went to her catholic counselor and wouldn't let him go with her and then she said the counselor said it was all my dad and that he only cares about himself so my dad asked if he could go with her next time and my mom just said no, i'm not going again. So how do you make someone want to try to fix things or try to get to the bottom of things? I can really see both sides and I really don't want my parents to divorce and I really think they need to go talk to someone or that they need to look at her medicine or talk to the doctor or something. I mean there has to be something that can be done. Also we have had the battle of addiction to alcohol and that's really not good to mix with the medication and everything so really I just don't know what to do from here. Has anyone been through this sort of thing? Like the person after treatment and everything is just not happy and won't do anything to fix it or that they think that nothing is wrong like they aren't being negative but that everyone else is ganging up on them? I just don't know where to go from here or what to do, any advice would be very appreciative and I thank you in advance.