Had Japan not accepted mail for a while after the earthquake, and are they accepting mail now?

There is no problem in Kawasaki. Fukushima has Fukushima Plant. So some of residents have been ordered to evacuate. Some areas are still exclusion zone where people are not allowed to enter.

So it depends on where in Fukushima her mother lived.

I live in Tokyo, several weeks after the quake I ordered a book from England (just checking if anything was arriving from there) and it arrived just fine within a few days.

I also tried sending flowers to my mother (a customary in Japan for the mother's day) who lived in Ibaragi, where there was a huge earthquake, and they arrived alright, and I got a thank you letter from her, again after a couple of days.

Sorry I have no idea about Fukushima and Miyagi, where there were most damages from the tsunami, but we are donating tons of money, just like those people from other nations, we are not eating or using much electricity, and those ppl who are affected by the tsunami are supposedly having enough food to keep themselves alive, so I suppose they are getting stuff from other areas from overseas as well.

you can send and recieve mail already since the day after the earthquake.

Any kind of mail are ok now.