my first was 26 months when I bought home #2, both girls. #1 was so gentle and loving <img src="/images/graemlins/smile.gif" alt="" />
Several years later when they were 6 and 4 we brought home girl #3..they were fantastic, but also older.
THEN, when #3 was 19months old we brought home #4 and let me tell you...it has been a struggle since! It's been 6 months and only now is she not hating her little brother. She started nursing again when he came home, she started hitting and biting everyone...it was horrible.
I think, however, it had a lot to do with her overall attitude, so don't let her reaction scare you. Kid #1 is so easy going, she always has been. Kid #3, not so much, she is needy and spirited and cranky and opinated and darnit, she wants to be the baby!
Good luck!
meg