What does Linda think is the trouble with Willy’s life? and why is she angry at her sons?

Linda knows that Willy is depressed.  He is overworked, he
still has to travel for his work, he is working for commission.  He has had one car
accident that seems suspicious, and he is talking to himself.  She has found the hose
that he wants to use to kill himself with.  She also knows that he is not only
disappointed in his own lack of success, but he is very disappointed with Biff.  Biff is
in his thirties and he still hasn't found himself yet.  Willy goes from calling Biff a
"lazy bum" one minute to a god the next.

She is most angry
at her sons because she does not think they pay their father the proper respect.  She
wants above all else for Willy to be happy, and she does not want Biff (or Happy) to
upset him with the truth.  She prefers that they cater to Willy's illusions of their
success.  When they leave him alone in a restaurant, Linda is furious with them.  She
does not think they treat him as they should.  And she refuses to let Biff talk
negatively about him.

Linda desperately wants peace in the
family, but she probably sacrifices too much for it, and she is ultimately
unsuccessful.