"She is reading."
That's actually a deep question. It is because קוראת is a form of קרא and אוכלת is a form of אכל. Edit to explain further: the א comes from the root of the verb.
I'm not sure why, but the א is silent. It is the same with all verbs whose root ends with א, in this case the root is קרא.
my mother tongue is Hebrew... its not the smartest language... XD there are a lot of different weird exceptions, and basically every case is different...