As per the asked question, there can be three different cases, which are given below:
1) P and Q are standing in the same row.
Through the question, we already know that Q is the tallest in her row.
=> Q is taller than P.
2) P and Q are standing in the same column.
Through the question, we already know that P is the shortest in her column.
=> Q is taller than P.
3) P and Q are standing in different rows and different columns.
In this case, let us assume that R is the girl standing in Ps column and Qs row.
Here, Q will be taller than R and R will be taller than P, which implies that Q is taller than P.
Therefore, in any case, Q is taller than P.