Hi and welcome to the forum Robert,
Sounds like you and your neice are doing all the caring, and what a terrible worry the situation must be for both of you.
Two things I noticed from your post that could explain the highs. Firstly the meal prior to the 16.4 rise, was very high in carbohydrates. Potato, carrots and parsnips together would cause a BG rise. Personally I'd only have one of either with a meal.
The other thing, and you made reference to suspecting it, is Lantus :twisted: Dreadful stuff for some people, including myself, and you don't need to look far on this forum to find others suffering not only erratic, inconsistent and unpredictable BGs on it, but pain,digestive troubles, exhaustion, etc;....
Here's some link about both that you might find useful
brianmac.co.uk/food.htm#P
viewtopic.php?f=26&t=2797
Keep us posted on how things go with your sister and her husband.
Jus
Edited post to put UK carb counting web-site on.