Should I take a certified check?

I' M SELLING A COMPUTER SCREEN AND A HP PRINTER WITH INK AND THE CONNECTION WIRE FOR THE PRINTER FOR $60 ON CRAIGSLIST. THIS LADY HIT ME UP ON MY EMAIL SAYING SHE IS INTERESTED TO MAKE A INSTANT PURCHASE AND IF I'M SELLING THE ITEMS TO HER TO TAKE MY AD OFF CRAIGSLIST. SHE OFFED MY $60 PLUS $30 FOR ME TO HOLD THE ITEMS WELL I WAIT FOR A CERTIFIED CHECK IN THE MAIL AND IT CLEARS.SHE IS SENDING $990..I'M SUPPOSE TO CASH TAKE MY $90 OUT THEN GIVE THE REST TO THE MOVER THAT ARE GOING TO PICK UP THE ITEMS BECAUSE SHE IS TO BUSY HERSELF TO PICK THE ITEMS UP..SHE SAYS SHE IS A NURSE. WHAT SHOULD I DO?????????????