How do you care for an elderly parent who is constantly angry, unhappy and always complaining - nothing done for her is ever enough...

At this point, she isn't going to change. You are going to need to. It has nothing to do with you. Its just how she is. Tell her what ur willing to do and not do. Trying to make her happy will not work.

How do you care for an elderly parent who is constantly angry, unhappy and always complaining? YOU DON'T!!! Either Mom does it herself, or she hires someone to do it for her. Period.

"Oh, I couldn't possibly do that well enough to please you, mom. Hire someone to do it and you'll be much happier with the professional results that you'll get".

Honestly..... you stop. Only do what you WANT to do for them. No one is owed care. Next time they complain about how you do something, tell them to find someone else to do that.