Have you done much research into that area? Do you know if there's a brand we should check out or any common gotchas? (I can't find much reasonable info on this online due to my poor Google skills and all the bad info out there..)
1. Wait 24 hours, the CGM needs time to adjust to your body
2. Don't overcalibrate in the first 24 hours, or when sugars are in flux. You'll mess up the factory calibration which can lead to worse accuracy over the session.
3. Try a different insertion site. Behind the arm and on the abdomen are the two most common ones.
4. Talk to your endo
5. Call your CGM maker, they will almost always overnight you a replacement if it's demonstrably failing.
It used to be that they (older models) were off by huge margins, and the auto modes had to be constantly calibrated against as it was often not only off, but suggesting/dosing dangerous amount in either direction.
Nowadays, SO calibrates a few times a week and the pump is extremely reliable. Longer periods of highs are usually due to infusion set leaking (eg. line snagged and pulled the needle).
Like the other reply, it takes a day or two until the system is reliable.
Sensor on back of the arm, infusion on stomach is the combo we've found to be the most safe and reliable sites. Make sure you rotate as often as possible and avoid putting them in the exact same spot.
Calibrate it several times when her blood sugar is stable. (Stable means not changing. I want to see a line on the CGM like this "-------------" not one that is going up or down.)
Make sure your test strips and CGM sensors are in date and have been stored at reasonably indoors temperatures.
Source: My wife and I both use CGMs. Our common medical issues were something we had in common.