Well, IF they find the pics (and they get paid to find some OS or hardware failure, not to browse your pic folders!), it depends on several things:
a) Will they report anything? (Chances are they'll look at them, exchange some jokes and give your PC back without reporting anything...)
b) Will they SEE she's 16? Nowadays, with 13-year-olds running around looking like an overdressed 17-year-old, who can tell which age someone has?
c) Which country do you live in? Everything depends on the laws your "case" would be subject to if it will be reported (and it won't!). In most civilised countries a 40-year-old taking pics of a 16-year-old girl might be in trouble, but an equally aged guy won't. In Germany, girls of 13+ years of age are even allowed to have a sexual relationship if (1) their BF is of similar age or (2) their BF is 18+ but the girl's parents don't object. In a country with such an ultra-conservative, hysterical (and hypocritical) attitude towards the sensual & sexual sides of life as the USA, I don't know what the situation is, though. If they are capable of breaking into a house fully armed and tear a little boy out of his mother's arms holding a gun against his head (probably causing a life-time trauma!) just because a peeping neighbor accused the boy of having taken a look under his little sister's skirt, I guess everything is possible.
But don't you worry, I'd bet 85% they won't even see the pics. You know, if the were looking for stuff like that on every PC, they'd have to work 20 extra hours a day. (I bet there are some nice p0rn collections on private HDs...)
And the other 15%? Well, I'd say 10% they see it and don't say anything, 4% they see it and make a stupid comment or a broad grin when handing your rig back to you, 0,999% they'll report it and nothing will happen and 0,001% you'll get some kind of warning, that's it.
EDIT
As for that "pedo stuff detection routine"... I wouldn't know how to detect pedo pics on a given HD in any other way than finding & looking at every single image file. This can take ages, and repair services don't get any benefit from it. It only costs them time and money, so they won't even be interested in searching such stuff.
Actual pedos are caught 90% by credit card number identification (when they paid by credit card to get into a pedo site). They trap some more in cafés and restaurants where the pedo they've been monitoring on a chat room has agreed to meet with a girl (who might be an FBI agent who's in the chat room for no other purpose than trapping pedos). And they get many of those bastards who really hurt or even kill a child in real life (too little and too late, but at least many). Oh well, and I suppose if they monitor your internet activity, get your IP (from a "sting site", i.e. a fake pedo site put up to catch pedos) or something, they may get you, too - depending on how openly you surfed the web.
But your case is totally different. First of all, you ARE no pedo, and secondly there is not a single trace that would lead anyone to believe you might be one and search your stuff. And once again: The repair service has no interest whatsoever in wasting time to search your stuff, and no resource to detect what's depicted on the Jpegs you have - no other resource than their eyes, that is. Relax...