dont you just:
[ln(x-x^3)] from -2 to -e
and you get ln(6) -ln(-e+e^3)= ln(6/(e(-1+e^2))) = ln(6/-1+e^2) - ln(e) hence that girls solution ln(6/e^2 -1) -1
im pretty sure she didnt want the u substitution method but its better that you show your supreme ways sy ;)