The SAS similarlity theorem is the type of similarlity that show that two triandles are similar by showing that two of the sides are similar with the angle between the two sides also similar.
Thus, given that segment ST and segment VW are congruent, and also from the image it can be seen that angle S is congruent to angle V.
Thus, to show that ΔSTU ≅ ΔVWX, we have to show that US≅XV.
Therefore, the step that could help her determine if ΔSTU ≅ ΔVWX by SAS is US≅XV