Ohhhh! You're right! I left the previous command in the description 😁 Thank you so much for the report!!
Try to control your hold and click to always leave the big bar in a point where her pain bar growing the lowest possible, so she can grow her flexibility without overdo herself ^^
I'll be adding the following description to a minor update soon.
"Click and hold the screen to stretch the girl leg, and release it to release the stretching. Control your holding and releasing time to increase her flexibility by 100% before the time ends, without leaving the pain bar reach 100%."