The letters on the tiles are W, I, S, D, O, M.
First, we identify the vowels among these letters. The vowels are: I and O.
There are 2 vowels (I and O) and a total of 6 letters (W, I, S, D, O, M).
To find the probability of picking a vowel, we use the formula:
\[ \text{Probability} = \frac{\text{Number of favorable outcomes}}{\text{Total number of outcomes}} = \frac{2}{6} \]
Now, we simplify the fraction:
\[ \frac{2}{6} = \frac{1}{3} \]
Thus, the probability that the letter Abby picks is a vowel is
\[ \frac{1}{3} \]