They treat her like this because they know they can get away with it.

People always say, «there’s no wrong way to grieve,» but as a society, we don’t really believe that. If a mother brings up her son who passed away days after he was born at every occasion for 20 years after his passing, people would not think she has grieved in the «correct» way, and maybe they’re right. It’s probably not «correct» to never get over the loss of a family member, but it happens all the time, and sometimes there’s nothing one can do about the grief that does not subside, no matter how much time has passed or how much therapy they have attended. 

As a society, we give people who have recently lost a family member much more leeway. If your brother passes away and you work somewhere that isn’t downright terrible, they will give you some time off to grieve your loss. Of course, the amount of time you get from your employer is usually never enough to fully go through the grieving process. Heck, it takes decades for someone to fully «get over it.» But a workplace shouldn’t force an employee to come into work when they literally can’t stop crying about their loss. That’s extremely uncouth.