What was it with them thinking the super's wife was in a wheelchair?
I totally didn't get that. Why did they think so? What was that all about?
shareKate mistakenly believed that the woman was in a wheelchair. She usually felt so bad about 'less fortunate' people that she imagined their situations to be worse than they really were--like the super's wife or the young woman with Down's Syndrome at the gym. This young woman seemed happy enough, but Kate looked at her and started crying (not too good for the girl's morale). That's why the head of volunteers told her to leave.
This was just a symptom of her shallowness. Because Kate thought herself so fortunate, everyone else had to be 'tragic.' Her good fortune didn't make her that happy though; she kept giving but didn't feel better. That's because she was essentially a vulture, robbing the unwitting heirs of valuable items because they wanted to sell their relatives' estates quickly. Kate and Alex made their living off of deceased people's belongings, buying the items for a low price and then inflating their worth so that other shallow people with disposable income could buy them.
Then Kate would feel guilty and give money to the homeless or try to volunteer. The one thing she wouldn't do was to change her job; that would mean not having a high quality of life and disposable income, with which she could buy her teenage daughter a $200 pair of jeans.
"And all the pieces matter."
You kind of got it right, but her I think the reasoning to buy her daughter the $200 jeans is off. First of all, she gave because of her liberal guilt, not necessarily for the less well off's well being, but that giving doesn't seem to alleviate what is lacking in her. That is why when she went to volunteer, she can only feel guilt and depressed for them, without the notion of actually helping them. It is the same reason she does not buy her daughter the $200 jeans. She does not give to make the other person happier.
It is only at the end of the film, where she buys her daughter the jeans, do you see a smile on her face because the person at the receiving end is truly happy at the gift. That is also what the workers at the nursing home and children with special needs center are looking for (which is give for their sake, not yours), and which Kate did not possess until we see that glimmer at the very end.