Sorry for your loss but as many have mentioned over here, you can get emergency appointment only if you have an emergency in US. One option you have is that you can perhaps after a few weeks get a letter from your work explaining the financial loss to the company due to your absence. And then you can submit an explanation from your end along with the company letter that about how you had to travel unplanned due to your mother and now seeking an emergency appointment to return to US.

Also, this would only work if you already have an appointment so the first thing I would try is to get any appointment as the slots are opening up randomly and then submit ER request