Unfortunately I don't have much experience with security suites, I tend to go more down the multi layer route and combine different products, or sometimes not run anti-virus and a third party firewall at all. What I would say is that there probably isn't a security solution out there user friendly enough to not trouble the most noobish PC user out there, it may be worthwile getting one and then taking a little time to show her how to use/configure it properly. (they may be old, but they ain't stupid, lol) There are ones that can be a real pain to use, ie Mcafee (at least the 2004 version was for me) Zone Alarm can pop up seemingly every two seconds from what I remember, so a 'user friendly' solution can be less talkative, but then this can raise questions about their effectiveness. Most will have options of what to allow/block from accessing the network each time you open something that requires access, so it's either up to you to configure these for her, or show her what applications she should allow or block. (I tend to just click allow each time whilst shouting 'GO AWAY' like a man possessed.

Works all the time lol.
I would recommend installing Spyware Blaster, especially if she will be using IE, it's a simple security solution. I think the payed version has the automatic update feature which would further simplify things as the user wouldn't have to do a thing. I think this is only really necessary for Internet Explorer users however. Install something like AVG or Avast, they should scheduele a time and day to scan and will update automatically, so that's not much of a problem.
Sorry I couldn't be of more help, but hopefully that's given you some ideas. Google some security suites, read some reviews etc etc. That should help make your mind up.
