I work in events and coordinate several weddings a year as a side business. I can tell you what I normally do with clients the month prior to the wedding, just to give you some more information that may be helpful. Keep in mind that every planner is different and will offer different services, so your friend will need to know what's really important to her that the planner cover. Pretty much client I've worked with has hired me not only because they wanted day-of support, but because they had some specific logistical concerns they needed addressed (shuttle buses, getting guests to and from different wedding sites, event happening in a public place, etc.). If your friend has any of those issues, it's important to bring them up in an initial meeting with a planner.
In terms of hiring a planner, I think word of mouth is the way to go. Ask friends who they used. Her venue may also have a preferred list of recommended planners, but I wouldn't hire one without talking to a previous client of theirs and getting some first-hand info on their strengths and weaknesses. Also, a good planner is usually not the cheapest planner. You don't have to spend a fortune, but that "planner" advertising a $500 special on Craigslist is probably not the right option.
So, I really don't do only day-of coordination. You can't just drop into an event at the last minute and confidently be in charge of the proceedings. There has to be time for the planner to get totally up to date on all the logistics, tour the venue, talk to the vendors, etc. For me, this starts about a month out. Maybe 6 weeks depending on the complexity. These are the things I would then include in my services:
-Meet one month prior to your wedding date to review wedding details, gather information and discuss your needs (This is usually a 2-3 hour meeting, and I like to do it at the wedding venue if possible. If not, a separate venue tour will need to be arranged)
-Provide advice and consultation via phone and email in the month prior to your wedding.
-Obtain copies of your wedding vendor contracts and confirm the specifics with your vendors. (I am really familiar with contracts, so I flag anything that seems unusual or uncool for the bride. I also talk directly with the vendors to confirm all the details, their arrival specifics, and the fact that I'll be their contact going forward).
-Create a detailed timeline for your wedding day. (Essential!)
-Attend and direct the wedding rehearsal. (If someone else is directing the rehearsal, like an officiant, I simply attend and make sure I get to know who all the wedding party members & family members are)
-Collect all personal items, such as programs and toasting glasses, at the rehearsal and deliver them to the wedding venue.
-Coordinate vendor setup on the wedding day. Ensure that all contracted items have been delivered and properly placed at the venue.
-Assist you, the wedding party and family members with any last-minute details on the day of the wedding
-Distribute final payments and gratuities to vendors.
-Coordinate with the photographer to make sure all your requested photos will be taken.
-Decorate your bridal suite (within 5 miles of the wedding venue).
-Collect gifts and personal items after the reception and deliver them to a designated person or location.
All the brides I've worked with have been very organized and I've just been able to run with the plans they've already put in place. If I came into a situation 4-6 weeks out where there were vendors still unbooked and plans still not solidified, I would charge additional to support that.
In terms of a planning book, I don't think you need anything more than a simple binder to collect your information. I know there are some fancy, expensive systems out there, but honestly a binder and some checklists from the internet will do just as well. Let me know if you have any questions!