I've spent hundreds of nights as a single woman wild/permissive camping and rarely felt threatened. At the end of the day my camper, locked up, is probably more secure than my house and I don't feel threatened or unsafe in that.
A few tips. Make sure you always have an exit, difficult to be blocked in, reverse back against a wall for example leaving a gap so you can manoeuvre but not big enough for another vehicle to get behind.
Don't park where you can be obviously seen from a main road. In fact, for aesthetic purposes, don't park where you are likely to be seen, full stop.
No external blinds at the windscreen, only interior so you can drive off without getting out, and drivers seat facing the right way, not swivelled.
Keys where you can find them: something to make a lot of noise:: Phone to hand.
There is nothing more magical than waking up with no sign of human life other than your own and to go leaving no sign of human life ever having been there.