I don't find Dee's powers are to be considered lacking or shown in poor light in the ambulance scene. Just think about the weight she was holding back from toppling down.... How many were there in the Ambulance almost the entire Shergill family. Let us think of the approx weight...
Mahima 70 kg, Oj 65, Ash 60, Sim 56, lava 58, Rashi 58, Oj's second daughter 56, nurse 60, driver 70.... That is 500+ kg.
How is it any way showing her power in poor light?
Aj along with his own strength just added a bit of science too into it, to pull back the van that was already held stationary.