Her family (the Lovegoods) was mentioned in Book 4 - HP and the Goblet of Fire. However, she first appeared in Book 5 - Order of the Phoenix and she also appeared in books 6 & 7.
it's your opinion, i like harry potter and the goblet of fir the best personally but whatever of the fantastic books is your fave. All seven of them are books, if they weren't, they would be called...