Predicting sugar levels in the US vs. UK

My gf (T1) is from the UK and uses a pump for which she has always done a good job managing, however each time she travels across the pond to she ends up with consistant highs / lows.

It's obviously frustrating for her and as I'm sure many of you have felt the same, she feels upset an depressed that she can't seem to keep consistant levels.

My initial thoughts are that even though she makes good food choices the US generally has a ton more sugar even in basics. Whether it is fruit, salad, pizza etc. It seems hard to get it right.

I suppose I'm looking for other thoughts and opinions on this. Has anyone else traveled like this an delt with the same thing? She is not on Reddit ( I'm trying :) ) but I think it may help for her to read a bit about others dealing with the same struggle.