Be firm, need to put her in the situation without putting her in A situation, get the help of a child, maybe to give her treats or something show her that nothing bad is going to come of it? The car situation imo isn't a complete bad thing you got to ask why there's folk that you don't know/she doesn't recognise approaching your motor, none of mine had any real contact with young children till they well on, they got put in a position and had to deal with it, they were wary at first but soon realised that it all can't be bad.