What I would recommend is scanning the buffet and making a decision as to what she wants to eat, determining the carb count and then bolusing 15 minutes or so ahead. In a way a buffet is easier than a menu,because you can actually see what you will eat. The only catch with buffets is you have to be disciplined enough not to get seduced by the "all you can eat" siren and go back for more. If you can't resist, then just go ahead and do another bolus to cover the seconds and be sure and check at 2 hours to see if you're high.
I think the pump makes buffets or multi-course meals that are served over time easier...just bolus as you get each plate. The nice thing about a buffet is you can control the portion sizes and what you eat...you aren't stuck with a big pile of mashed potatoes or rice, etc. Get a plate, bolus for what is on it, get the next one , etc.
As far as pre-bolusing, you might do something safe and assume you will have some bread or other carb easily available and pre-bolus for 15 or 20 grams. You don't have to eat that...just subtract the amount you prebolused from your first trip to the buffet. Personally, I would be hesitant about pre-bolusing for the whole meal up front as you don't know what will be on the buffet or how much you eat.
I find that the BG numbers frequently work out better with a multi-course meal or buffet than with getting all the food at once as the eating is spread out over time and it gives time for the insulin to start working.
Oh, I was assuming this was the kind of buffet that is already laid out so you can look and see what you want to eat, bolus, wait, then go back and fill your plate, rather than eat it as a multi-course meal.
I was just saying you could treat it similarly if you want to...go to the buffet and get salad, bolus, etc, go back and get entree, bolus, etc. Yes, you are right, if you can decide up front and limit yourself, bolusing all up front would work too.
I just put food on my plate until it looks like a normal meal and bolus for it. If it's a party with all kinds of finger foods I will set a extended bolus for a couple of hours = my carb limit and when I reach that point I stop eating...It's never perfect and sometimes I spot something I just can't pass up and do a standard bolus on top of the extended bolus.