I work with someone who is extremely miserable and moody. At the beginning I was really lovely to them as they had anxiety (as I do) so was very helpful to them and very supportive.
Three years on and I think she is just a very rude and miserable person. She brings down the entire atmosphere of the office and it is really effecting me. I love my job but being alone with her in the office when other colleagues are off fills me with major dread. Most days she barely says two words to me and almost answers back when the boss asks her to do any task. She claims she had no friends in her old job and that colleagues ignored her.. But I'm starting to think there are two sides to this story. She acts as if she is the busiest person in the office when we are all equally as busy (I would say her the least so.)
She is rude to everyone on the phone, only ever talks about herself and interrupts when you try to help and give advice (never asks about anyone else) . It's got to the point where I don't make any effort with her at all as all she talks about is herself and it's never cheerful.
I really don't know what to do anymore, there is no HR department as its a small company. I'm also a lot younger than her so feel it's a lot to deal with 
. I just want to enjoy being in work.