African Frauds

help!

Hi,
first of all, thanks for opening my eyes.
My name’s Marianna from Slovakia.
The problem is, my sister received an email like that and tried to help the girl named Mercy Tamba from Senegal. Although my sister couldn’t help her because she was not 18 yet, after some time this Mercy wrote to my sister, that she is now in South America married to a guy who helped her.
However, she wanted to thank my sister for all her effort and left a check of 2,5 mil. dollars for her at Rev. Kennedy.
And there it all began. First, only 200 EUR was needed, then he needed some more for an insurance and next the IMF (International Monetary Fund) wrote to my sister, that if she won’t get the Antidrug certificate, both she and Reverend could be prosecuted.
There’s a kind of deadline until Friday or what.
I am scared – is it really the IMF who was writing to her?
Reverend sent a copy of insurannce, but I don’t believe they are not artificial as the data in the down left corner is wrong – my sister began writing with the girl only in 2008 while the data written there is 2006 and 2007. I doubt also because the English of someone from IMF should be simply better and more formal.

If you can help me anyhow, please write me soon. And thank you.
Best regards
Marianna