Agree there is no single 'best' format, the golden rule as far as I'm concerned is to take the time to tailor your CV and cover letter to every role. It is very, very obvious when people don't do this and are just banging out the same letter for every job.
Have a snoop around on LinkedIn to see how people in the relevant industry/profession describe and set out their skills.
Use bulletpoints on the CV and think about how well you're representing not just what you did, but how well/competently you did it (anyone can be the first point of contact for customers, not everyone can provide excellent customer service to everyone who contacts the business from Directors to contractors, customers to suppliers).
Pay attention to whether they're asking for a covering letter (more of a courtesy) or a personal statement (a letter addressing how you meet the required and desirable criteria for the role). If in doubt, go with a personal statement.
More one for the future in her case, but don't leave gaps on your CV. The recruiter will be using it as a timeline and gaps look more suspicious than leaving a role after a couple of months.
Treat the shortlisting manager like a tired, hangry toddler with the attention span of a butterfly - make your application as clear, brief and idiot proof as possible. If you're asked for a CV and personal statement or a CV and application form, make sure that both have the information in them that will tell the recruiter you have the requisite skills. Rightly or wrongly there are very few people out there who will still be reading applications as thoroughly and enthusiastically by no.80 as they are when they're on no.1.