The reason sheila put her hand through a window was because she found out colin had been unfaithful, he had been drinking and when sheila tried to question him about it he ignored her and tried to go to sleep, sheila was furious (understandably) and put her hand through the window, she did this more to get a reaction from colin, because colin reacting reasured her that he loved her.
sheila also used to smash colins pottery(prized possessions) during arguments, she once did this to a particular piece, and it resulted in a black eye for sheila from colin. Colin carried guilt for that for a long time.