Natasha Whatley and Caitlin Lowe are both in the 2.6 second range and they are the 2 best in the world. So that would be a good target for your daughter to start working towards and she'll have a great career.
I work with a lot of slappers and they aren't there yet. I assure you.
Generally I look to work with girls that are "fast" for their age, and they are athletic. Hitting a ball while you are standing completely still is difficult enough. But trying to move your feet and adjust what your hands do for each pitch and still hit a moving target towards a particular open spot on the field is REALLY ... REALLY tough. So speed is nice, but athleticism and confidence are also required when considering the move to slapping. The nice thing about starting girls young is that they can build their confidence against weaker pitching and weaker defenses so that when they do face stronger pitching down the road and good defenses they'll have the confidence and the practice to be able to put the right slap on each type of pitch in each situation.
Gold level and college you better be that 2.6 or really better if you are a pure slapper IME. You can be quite a bit slower and still be effective if you can slap or hit for doubles power along with playing the short game. It's like running the option in football. You just take what the defense gives you. Then the pitcher has to keep you from executing.
If you want to give your daughter the best chance possible, you need to work on all aspects of hitting. A pure slapper/bunter will enjoy some success, but defenses can adjust to it and take away alot of the slappers advantage. But, send a girl to the plate that can drag, slap or hit away and the defense has absolutely no clue how to play her. Play for a drag bunt and she will slap, play the slap and she will swing away, play back for the hit and she will drag or slap.
Hit away or be able to hit with pop on the move-either one is good enough. I love a kid who can dump it short or lace it down the left field line just over F5 for a double and do both on the run... but I'd be happy to have the kid who can stand and smoke one with a standard swing on the left side as well as playing the short game. One of the most fun to watch and most effective left siders I ever saw was 3.0 home to first in games from contact (very small college but I believe she could have taken her game to a bigger stage). But...she placed that ball like a pool shark spotting the cue ball. Where ever you played her was wrong on the short game and if you collapsed in on her with the outfield, she'd put it behind your F8 on the run. Somewhere I've still got a mini DV with a bunch of her AB's. Not on my side but I found it interesting watching her be so effective with so little speed.
I have a dd that is 2.84 an 14U. I have to agree with the posts above that being able to hit for power along with slapping is very important. Learn to bunt, then slap, than power slap. Then learn to hit for power. This all takes time, but makes you a very tough out for any defense .