OMG you poor things
well it seems obviouse that it IS due to being hit by the truck
i too would definitely NOT go back to nappies, yet!
Just a double layer of bed sheets etc to make the mid night changes as stress free as poss, so waterproof sheet, under sheet, bed mat, another under sheet, so wet mat and sheet can be whipped of quick, with another nice dry one all ready in place
im sure lots of comfort and reassurance will help, and hopefully in time she will start to feel better.... maybe if it goes on for several weeks, you could suggest it and gae her reaction.... but if she doesnt want to dont push it.... being hit by a truck is a big enough 'punishment' already (not that she deserves to be o0punsihed!)
BTW im sure she is genuinely terrified... when i was 16 i was hit at 50mph by a car... i was very badly hurt (nearly died, then nearly had leg amupated, but thank god Drs managed to fix me!)
i remember for months afterwards i was terrified to cross roads.... i would wait for AGES until there were no cars at all even in the distance on the horizon... sometimes cars would see me on crutches and stop to let me pass... but i just could NOT walk in front of even a stationary car... so they would stop and 'wave' me across (seing my crutches).... and i would freeze with fright and not go!!!
even now im cautious and never take risks.
be patient with her! Im sure she will find walking even on the pavement VERY frightening for a long time, and even now (9 year later) if a lorry or something goes past fast and close to the pavement it can still make me jump.