Important questions regarding my 2008 tax return. Please help!!!!! 10 points to the best answer?

ok i have a child and 1 paid my cousin $3000 for the year of 2008 and i claimed it on my tax return, my cousin is 22 and she is no public istance, does she have to claim the income, if so where does she claim it on her tax return if i never gave her a W2. another question I already did my tax return but i didnt include my extra income i received from my mutual funds becuase i just received that letter in the mail yesterday. will i be penalized or can i claim it on my tax next year? if not what do i do if i already sent my tax return and they accepted it ( it was e-filed)???