Yastika's problem, despite her scores of note, is the manner in which she gets her runs.
It is tough to fit her into the current batting order, or redundant in most scenarios.
Here's the why:
Of the 19 occasions where she's scored 20 plus,
1) 8 times, she's been dismissed within or right after the powerplay (indicated by a circle)
2) In only 4 of these innings, has she struck at less than 100 in the powerplay (highlighted in red)
3) In the 11 innings where she's gone past the powerplay or batted considerably in the middle overs, she's slowed down 5 times (~45%). Basically, almost 1 in every 2 innings is a slowdown.