You could argue that giving her a PR briefing before she left the house was against the spirit of BB.They're meant to be cut off from the outside world with no idea what to expect when they walk out through those doors.

Will he give such detailed advice to the other three?

Jon did announce, whilst in the garden mid-week with Scott and Nush, that he would, indeed, be giving a little talk to EACH of the housemates before they left. This was seized upon on the board as evidence of 'Playing With Their Minds In An Evil/Brilliant (delete as applicable, obviously) Manner.' However, what if Endemol have told him to do this, as part of his guest role? Having come out and gone back in, who better to give them this advice?