It's sounds like a powershift transmission issue (failed clutch causing stall) that should be covered by Fords extended warranty but seemingly isn't on the lower volumes sold Mondeos ("Lemondeos"?) see
https://www.redbook.com.au/car-news/...?csn_tnet=true and
http://www.caradvice.com.au/546286/f...ould-you-take/
I would take it to a Ford dealer for diagnosis as having anyone else work on the transmission or related parts will kill any chance of Ford fixing it for free. If it is the trans and Ford won't fix it for free I would contact the ACCC.
Also see
https://www.drive.com.au/new-car-rev...d-mondeo-65107 was the daughter using hill-hold as recommended?
And yes; I also suspect it's the similar sounding engine/trans fault alarm rather than a reverse sensor.