Best Philly restaurant for non-adventurous eaters
Hm. Lolita (fusion) or Xochitl might be good for Mexican spots. Good food, both for the adventurous and non-adventurous eaters.
Standard American ... Matyson in Rittenhouse is a pretty popular spot around here, and it's solid American food. (This could be your upscale dinner.)
Davio's is an Italian steakhouse at 17th and Sansom. It's not exactly mindblowing food, but it's solid and good for a non-adventurous eater.
La Viola is a good Italian spot. I don't like it, but that's more of a factor of space & noise (La Viola Ouest supposedly takes care of these problems) than the food, which is quite good. Really, though, Philly's a good town for Italian food, just depends on how much you want to spend and where you're staying.
For gastropubs, there's always Good Dog (and who doesn't like a good burger ... that likes standard American grub).
I mainly stuck to the Rittenhouse/easy to get to spots since we don't know where you're staying. Perhaps you can clarify?
Upscale Italian I would suggest Osteria or perhaps Table 31 with its new menu.. Upscale mexican, perhaps the Starr restaurant El Vez or Tequilas.. You have a plethora of steakhouses to choose from (Capital Grill, and Barclay Prime being the best). Comfort food schtick at Jones might be fun for her has well.
I'd pick Tequilas over El Vez for someone "non-adventurous"....not that the food at El Vez is that radical, but if you order certain traditional dishes like tacos you might be disappointed by what actually shows up on the plate. Tequilas is more traditional (if upscale) fare.
There's Friday Saturday Sunday as well - one of the last remaining original Philly Renaissance restaurants left. Very nice (and affordable) wine selection, dependable menu, always had a good experience there.
Lots and lots of good Italian BYOBs as well - depending on where you're staying, could recommend a number of choices easily.