Unless it's winter, both are probably about the same; if winter I'd definitely choose CLT because of the weather issue. Philly used to be horrible, but the last couple of times we flew through there it had improved a great deal. Is she Global Entry? If not, CLT has kiosks for all passengers, which do help to lessen the wait at immigration (which shouldn't be bad on a Thursday anyway). I'm not sure if Philly has them; they didn't the last time I flew through there, but it's been a few years.