It doesn't match, of course - it's really either a studio matte or the Hollywood Hills - and suitably time-compressed that they haven't traded their Trachten for Johnson flannels yet, to say nothing about the kids not being any older - but it explains why they're walking in the "wrong" direction. They're headed towards Stowe Village, not Berchtesgaden.
- The valley behind them is recognizable as the Salzburg valley, and the gigantic mountain behind them is readily identifiable, for anyone who's actually been there. Also, the Green Mountains are nowhere near that impressive. And it's not a matte shot.
- Max told her that they needed to delay the ceremony as long as possible so the Von Traps would have time to escape. She deliberately took up extra time in order to help them, without going so far as to look suspicious.
- Some time after leaving the Banks family in 1910, she lost her powers and her memory and ended up wandering around Austria in the 30s. She retained two things: her passion for music and her talent for looking after children (and a distorted version of her first name).
- Or, going along with the WMG that Mary Poppins is a Time Lord, she at one point used the Chameleon Circuit to turn herself human, has forgotten her past, and will eventually return to Time Lord status.