I would see how they both get on and then make a decision from this. There really isn't a right or wrong thing to do because each situation is different. If they fall in love at first sight (well so to speak) and you feel happy leaving her 'free' with Mabel, then i would just let her sleep alongside Mabel but provide a seperate bed. If Mabel doesn't initially seem too taken with Esme then i would seperate them for sleeping. You will probably find that Esme will immediately love Mabel though,
as she will be looking for warmth/comfort/companionship/play after the upset of leaving her litter mate's and mum.
Personally, i have never used crate's, and never had any prob's.
apart from Alfie chewing the skirting boards.
Good Luck with settling Esme in her new home.