How do you know what they are capable of?

My mother has been depressed for about a decade we offered her to go to counseling and get medication but she says she is not depressed. My mother has never been one to express her emotions and it has gotten worse. She will say she is not feeling well and you ask her what that means and she can't tell you. We work her out every day for an hour. It includes walking the hallway in the house and doing the stair up and down 13 times. She is on oxygen on the lowest setting (she has COPD). If we did not work her out she would never move from her chair and just read all day. We bought her a bidet because she was not cleaning herself well and I typed up and laminated directions there are four steps that are labeled 1-4 and on the remote for the bidet (which is a large size) there are four buttons I labeled largely 1-4. I know that people might say this is the dementia thing but you have to understand my mother. A little under two years ago we had to take my mother in to the emergency room for a bad diverticulitis attack because she was bleeding a lot. They of course kept her because she had a UTI and other issues we were aware of she ended up in the hospital for about a week, but that night she was admitted to a room and then latter she had to share a room with a women who was older then my mom. This women was using a bed pan and was crying out randomly and screaming randomly. My mother who at this point never had an accident began mirroring this ladies behavior. She too began being incontinent and screaming out. My mother was such a drama queen that they had to move the two ladies. I spent the whole first night with her and she actually would intentionally wake me up with screaming if I fell asleep. I know this because she would be looking right at me when she woke me. She acted like she was completely helpless the whole time she was in the hospital and as soon as she got home she was back to normal. I was so disgusted with her behavior. So my problem is as she is aging these past few years I never know what she is or is not capable of because if you give her an inch she will take a mile. She would have someone do everything for her if we let her and she would be bed ridden if we let her, but how do you know when we are pushing her to hard?