There are a couple settings to consider, and even so IOB is still tricky.
One setting is the carb sensitivity - which is how many points 1 g carbs will RAISE BG. Your endo or pump trainer probably put in a 'default' amount if you didn't know for sure that 15 g will raise her 50 pts or something like that. (I actually don't remember what that is called in the pump.)
The next setting is the amount of time the insulin works - you could try knocking it down to 3.5 hrs and see if it makes a difference. In your scenario this would make it think there was more IOB than there actually was
The third is her target BG. This will have her pump correct her for anything 20 pts (or whatever +/- range you set.) above or below her target. the pump should be ignoring IOB in the total if she is within that range. You could try broadening the range.
If my son is 'grazing' which is what I would consider your example meal, I usually ignore the IOB unless he is low. I know the IOB is working for the carbs he already has eaten and give the full dose for the next item. Also, the type of food you are eating can mess with it. Burritos probably have a good amt of fat, so the carbs will be slower to digest (kind of like pizza) and so she might have ended up high later in the evening anyway.
Thanks! I did decide to adjust her sensitivity, though I adjusted it up, from 100-130, because I noticed she was constantly going low after corrections. I'm thinking I probably should have just used my head and added more insulin when she had the dessert, but it was close to bedtime and I'm always a little fearful of giving her too much before bed. Generally the pump settings work pretty well! I didn't really think about adjusting the range of her target, that's certainly something to consider. I did adjust her target down a little, from 135 to 125.
I do what you do when she's grazing. For example, if she's 71 before dinner we'll put in the carbs and let the pump do the first calculation, but if she decides to eat another 20 grams, I skip the bg part of the calc so it doesn't do it again.
Actually since the dessert incident she's been pretty darn good. Yesterday was insanely good, 153 at breakfast, 128 at lunch, 127 at dinner, and 130 at bedtime. Weirdly good! Today was pretty good too, 111 at breakfast, 88 at lunch, 190 at dinner (I think this was because she ate about 2 hours earlier than usual), and 160 at bedtime. Might tweak her I:C ratio back down just a smidge for food eaten after lunch, but will wait until the weekend because she has shows all week in the evening and being up on stage with all the lights and stuff tends to make her low.