Good job. Now, take a deep breath and relax. Although raising chicks takes time and dedication, it's not rocket science. If they have warmth, food, and water, and a place to go if they get spooked, they do very well.
If she's been chilled by the process, run a hair dryer (not on hot, high) over her to dry her and warm her up, then get her under MPH and turn off the lights so she (and the others) can finally get a full night's sleep. Sometimes even a few days after getting them home, one or two go sour and just fail to thrive. It happens. And when it does you take the best care of them possible and if they don't make it you put on your big kid britches and get on with taking good care of the ones that are left.
I have said that chicks I've raised using MHP outside don't seem to get pasty butt, nor do chicks raised naturally under a broody hen. But I have also said that I have no scientific proof of this - just my own observations. I had a few chicks in the last batch that came to me with pasty butt already, but one treatment for most and a second treatment for just a couple of them resolved it with no recurrence. That means that out of 23 chicks I cleaned 4 pasty butts once, and two of those twice. With my first batch of 23 chicks last year, raised under a heat lamp, I fought pasty butt in almost all of them....18 out of the 23 had it and had it more than once. So while what I said about MHP chicks applied to MINE, I simply can't say categorically that MHP has any kind of magic other than keeping stress levels way down and temperatures more gentle and even, and that is what I believe makes the difference.
Good luck!