Don't beat yourself up to much -- you're not a doctor -- they are the one's who should have thought of it earlier, not you! But I do know what you mean -- I think about it too because we were told 38 sweat test was normal, and nobody said a genetic test was available in the early 1990's - the internet wasn't nearly as prevalent back then, so I just took their word for it that it meant we didn't have to consider CF again.
If her sweat test is in the 20'-40's yes, specifically ask for an Ambry full panel test. I have an idea if she runs anything over 40 they will automatically call for it without being prompted by you. Yes, insurance in most cases will cover the test --especially if you have a borderline or positive sweat test number. You may run into trouble if she has a very low sweat test number - and at that point you may not want to push for it, because even the Ambry guy says "single digit test results" are unlikely to be CF (find two CF genes in testing) So if you get results back of something like 7, you are probably good -- but if they come back something like 30, you might have to fight for a genetic test. But again, since you are dealing with a pulmonologist at a certified CF center, chance are he/she will be knowledgeable enough to pursue full genetic testing on any suspicious sweat test readings.