Who becomes meimei`s new adversary in chess? why must she find someone else to play against

Meimei (Waverly) actually progresses in chess so much that she has many new opponents. At first, she play with her brothers - Vincent and Winston.  She quickly becomes better than the two of them.  Moreover, they lose interest.  If she is going to get better, she needs someone else.  

In the neighborhood there is a man named, Lau Po.  He is a good chess player.  She starts playing with him

well if u read the book you would know that she meant to