Undetected night hypoglycemia and CGM research

I have heard that Continous Glucose Monitoring has revealed that undetected nighttime hypoglycemia is more common than people think.  Because we use MDI with NPH and Novorapid and because her A1Cs are just below 6,  I think it is possible that we may be missing some night lows.  

What are Continuous Glucose Monitoring results telling us about what time nighttime hypos usually occur?  I would like to know this to make sure I am checking at the optimal time.

With a bedtime NPH injection at 10.p.m. (and some nights a bit of Novorapid for a larger snack or as a correction), what time should we do a night time check on our 11 year old daughter who was diagnosed one year ago, and below what blood sugar reading should we give glucose or a snack?

If you could lead me to any research results that address this, that would also be appreciated.

Thank you, Ashti

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I looked online at http://www.lantus.com/hcp/works/compared.aspx,  a site that compared NPH insulin and Lantus, which is a 24 hour insulin.  From the chart it seemed that the NPH peaked at 6 hours, so I would think that would be the time to check.
When you ask about the night lows are you afraid that her body is not signaling her to wake up and drink juice?  Is this happening a lot, I am just trying to figure out why you think you are missing these lows.  I use Lantus and I feel it works better for me.  I am wondering if a switch in insulin might help.  Every person is a little different in the way they react to insulin.  
It sounds as if she is fantastic control, under 6 is better than my HA1c.
To answer your other question, everybody is a little bit different too.  I feel like I need some glucose when my blood sugar is 65.  How does your daughter feel? I can tell when I am getting low, can your daughter tell?  Does she feel weak or hungry light headed?   I would think that 75 or below would be a good indication of heading for a low and needing a snack.
Have you visited www.jdrf.org,  it is the Juvenile Diabetes Research Foundation website.  I think it will give you a lot of the information you are seeking.