The soft tissue in the mouth heals very fast. You've only got about two or three days of soft food before moving on to "softer foods."
Avoid rice, ground nuts, chips, anything that breaks up into small, hard pieces. They have a way of finding the wound and lodging there. Just say no. At least for a few days.
Amazing Grace nailed a lot of the first-choice, very soft foods.
Don't forget matzo balls, especially as Passover approaches. There's a current thread on matzo balls here, plus there are a couple of good delis in West L.A. Fromin's which is bad on lots of things, does a good matzo ball. Zucky's and Juniors are very good. Junior's "mish mosh" soup, is a good idea too. It's a big bowl of chicken soup with noodle, matzo ball and kreplach.
Cook all vegetables down to mush. If you cook them in a little bacon fat, you can call them "southern style." Squash and carrots work very well this way.
Fish is soft. Back to Passover, does she like gefilte fish? Whole Foods is selling jars of Kedem (pretty good) for $4.99. Or go down to Santa Monica Fish Company, get some fish and make your own. Gefilte fish is a project which pays dividends down the line for a culinary student -- think quenelle de poisson. If nothing else, you'll learn to make a fish fumet. Gelson's has the best lox in Los Angeles -- or you can make your own gravlaks. Takes about 36 hours to get a real gravlaks going, but two or three full days is better.
Of course with smoked fish, you're going to have to forego bagels and real crusty sourdough (unless you cut the crust off). Plenty of good sourdough around.
Lots of sausages are soft. Several of the supers sell good bangers -- which are an excellent choice because they cook so soft. The place across from the King's Head on 2d in Santa Monica sells excellent bangers. Weisswurst cook soft, and so do regular hot dogs and knockwurst. You can get the best hot dogs in LA from the supers and meat markets in "Little Armenia" aka "East Hollywood." Jon's (alas) does not have the best, but they're certainly adequate. Farmer John Louisiana sausage are ground very fine, and are a little more interesting than a plain hot dog.
Barbecued chopped chicken and pulled pork are soft. The barbecue formerly known as "Benny's" on Lincoln in MDR is okay on pork and chicken. There used to be a "Texas" style barbecue on Overland, between Pico and Venice that was good for both and had brisket tender enough to qualify. I'm not a fan of Mr. Cecil's but you may be.
Hamburgers are fairly benign and they're definitely comfort food. Speaking of which, the whole surgery thing is pretty traumatic. It's likely her mouth will be pretty well healed by the time she wants exciting food. I'd start with "comfort," and move along slowly.
The most salutary thing is not to feed her, but to let her know she's special.