Yes it can be done when able to stick to hard facts but often HR take the route of no reference or simply start date/end date because they are afraid of litigation.
Bit naive of her to be shocked by this. Human nature unfortunately.
In many workplaces it's hard to speak out and I imagine being in the policeforce, like the Army, where you need your colleagues to have your back in sticky, dangerous situations, it must be even harder to speak out. Yeah...