Okay, let me summarize a bit:
You are restricted to the core book only. You want someone who solves problems with their brain, not their muscle. You also want someone who can socialize well, as well as possibly being a back-up healer.
Using the core book, I can really only think of three options.
Option 1: Bard. If you haven't had a chance to see what Paizo has done with bards, now is your chance. You can play bards so many ways, even restricted to core. You can focus on your spellcasting, support, skills, or possibly on your combat abilities. With a little work, you can do all of them pretty well, although not necessarily as well as if you focus on one. You don't even have to be a musician any more, if that's not the direction you want to go. Just use oratory (i.e. making speeches, giving advice) as your primary skill. Given the parameters of what you want, this would be my choice.
Option 2: Celestial sorcerer. A little harder to pull of the backup healing thing, and you are going to be hard pressed for skill points, but you will have more magical power than the bard option. This is also more party dependent, as you are only able to heal good characters. If you have non-good party characters, you will have to drop a level into another class, like cleric or druid, to heal. But then you will be 2 levels behind on spells compared to a wizard or druid.
Option 3: Druid. You give up the sorcerer spell list, but the druid list isn't so bad. Charisma isn't as useful as the other two classes, but with a 20 point buy, having a 12 or even a 14 charisma isn't that big of a deal. You are also weak on class skills for charisma, but that can be made up for with traits.
You also mentioned that you would play a summoner if it was available, so you could do a conjuration specialist wizard, if you want that to be your primary focus, dropping a couple of social skills in for flavor purposes. You won't be able to heal though, except through later game summons.
Since you mentioned that it is likely the game will not get past level 7 or so, I would NOT recommend mystic theurge. That prestige class only really comes into its own later levels, and even then it is a bit weak. Let's put it this way, you won't get your third level spells until level 9. By that point, both the wizard and the cleric are casting 5th level spells. Counting bonus spells from stats, at 7th level you will have 16 spells total you can cast (not counting 0 level spells), 5 druid and 11 sorcerer. A specialist wizard will have 18-19 spell slots (depending on if he has a 20 int or not by that point), including 2 4th level spells plus your specialization.
Hope that helps. if I am wrong in my summary, please let me know.
