The situation you have described is raising a whole lot of red flags.
First of all, you were contacted online by someone. You don't say if you know her, but i would assume that if you did, you would mention it.
Second, why couldn't this person cash her own paycheck? Why wasn't she issued a check negotiable in her country? Why can't she go to a US-based bank, or Western Union, to negotiate a cashier's check?
Third, by sending the cashier's check to you by UPS, rather than US Mail, whomever sent it is avoiding postal inspector involvement.
Fourth, there is a legitimate organization called IMEX - and IMEX is active in trying to stamp out various scams. Here is their website: http://www.imex.com/scam/bankcon.html.
If you Google "Imex Scam" you will find a lot of examples of people ripped off, by people who said they were affiliated with IMEX - but weren't.
This appears to be a rip-off; you will probably negotiate the check, send the money, and a few weeks or months down the line, be contacted by your bank to repay the amount.