If your friend is determined to get a pup through a breeder, then Midori has posted some excellent questions to ask on a recent thread about this, covering health checks and so on. Good breeders will not just have a pile of pups that you rock up and choose from - generally you can expect to go on a waiting list.
Your friend should think about the breed she wants and do some serious research into the health questions/scoring she should be asking. A good breeder will ask her why she wants that particular breed and if she understand the particular responsibilities associated with it e.g. exercise requirements, need to protect growing hips etc.
The access issue does sound worrying - is she really thinking clearly about how often a tiny pup will need to go out, especially at 3 in the morning? Rescues ask these questions not to be awkward, but because dogs do get stolen, get lost if gardens or egresses from doors are not properly secure. If you are in a shared area, then although you/your family may always close doors and gates for instance, there's no guarantee that other users will, hence the concern. You mention she has thought this through - if the solution is good, then I'd try another rescue. Actually, a good breeder might also be reluctant to home where there is not a secure back garden.
You can ask the breeder if they are registered by the local authority and if they are, ask to see their most recent inspection reports. Are they KC accredited breeders? Are they recommended by the breed club? Friend should approach breedclub in first instance and ask them for a steer/recommendation. Many breed clubs have breed specific rescues - maybe this could be something to investigate?
Red flags would include: adverts on Gumtree, Epupz or similar sites. Google the mobile phone number given - if it comes up regularly, especially if for different breeds then avoid. Avoid if they are unwilling to show you the pup with its mum or offer to meet you on the motorway to hand it over. Don't buy from pet shops or pet superstores. If you do decide to visit the mum and pups to see it, and they claim it is a family situation, then ask the adult lots of detailed questions about things like the worming regime, how long they've had the bitch, stud details, etc etc. Many puppy farmers place a bitch and pups in a home for the selling to make it look like a family sale - the home takes a cut off the sale and this also keeps HMRC off the trail. If you think the "owner" is in any way dodgy, then walk away. Ask them why they chose this breed, how long they've been breeding and what do they use the dogs for after breeding? Do they show/work the dogs? If not why not? Ask them who is their vet?
Do NOT take small children with you to view potential pup. It is your choice, not the child's and you should be concentrating hard on asking the right questions and looking at the dogs.