Depends on their area to an extent - I can find rescue across the country if needed but as long as the dog has no behavioural issues/ill health/is not of great age the Dogs Trust is as good a place as any to start with.
Breed rescue is another consideration - but FGS tell her to ensure that the rescue has a totally NO KILL policy.
If you can give me some details on the owner's area (county or nearest big town will do) and the age/sex/health/nature of the dog, whether he/she is good with DC and whether good with other dogs, whether good with cats and whether neutered and up to date with vaccination I'd know where to start and can probably help. It would help to know the reason for rehoming to, by pm if you prefer, for the benefit of giving rescue the full picture. (You never know, we may even between us come up with a way of helping the owner keep her dog). :)
Regardless of where the rescue might be, the main things to remember are, as I said, a NO KILL policy, a rescue which homechecks, assesses the dog, neuters/vaxes before rehoming and to start looking ASAP as rescue spaces can be hard to come by for the general public, with long waiting lists. To be fair, a LA is going to be a damn site easier to place than a poor old friendly staffie, but still it's harder for the public to do so than it is those of us who do this sort of thing day in day out, so as I said, if I can help, I will.