The excerpt is from the top answer on 知乎:
According to MDBG dictionary:
什么 what? / who? / something / anything
I guess the 什么 here means "what the hell" or something like that. So the meaning of the entire sentence is something like the following:
How can she use her husband's toothbrush to brush a toilet every day
But is my understanding correct here? What is the meaning of 什么 here and can it be used as such? Maybe more explanations about the usage in general would be helpful.