A student is asking about zakaah; her income is $400 per month

1-The time when zakaah
is due is when you have kept the money for a whole year. Then zakaah becomes
due, and the rate is 2.5%. This amount that you get every two weeks is not subject
to zakaah unless you have kept it for a whole year, or it is income from a business
for which the time has come to pay zakaah.

2-Pay your zakaah
in the country in which you live, if there are poor people there. If there is
another country where there are poor people who are in greater need than people
in your country, then it is OK to give your zakaah to them.

3-Yes, the one who
receives the zakaah has to be Muslim, except in the case where there is a kaafir
whom we want to encourage to become Muslim. If we think that that is most likely
to encourage him to become Muslim, it is permissible for us to give zakaah to
him.  

Shaykh
Sa’d al-Humayd.  

This
applies if that kaafir has a high status among the kuffaar and we hope that
by his becoming Muslim his people, tribe or clan will also become Muslims.  

The lowest amount at
which zakaah becomes due varies according to the type of wealth, whether it
is gold or silver. You are undoubtedly asking about an amount of currency such
as dollars. It appears that the amount mentioned in the question will be subject
to zakaah if it is kept for a whole year, because it is more than the nisaab.
For more information on the nisaab see Questions #2795
and 64.