Please don't find this odd, but, yes, we've had similar problems and have researched a few solutions. First, string bikini style seems to work better - the "strings" stretch better than more structured ones. Second, Victoria's Secret ones seem to work better too, as the elastic is "softer" and "more stretchy" and the cotton in them is softer as well and seems to stretch a bit better. Picking the right size was the other key factor. Although DD is a size 2 to 4 in Abercrombie jeans (i.e. is fairly slender) - the lovely ladies at Victoria's Secret told us to buy her Medium panties, as her butt, being a skater, is out of proportion to her waist size etc. So, we bought a size up from what we would normally be thinking would fit.
Other brands that seem to work are the GapBody ones, again, in a size larger than expected. When they go on sale, we stock up; same thing with the Victoria's Secret outlet stores
Victoria's Secret and GapBody do have tasteful styles that are pretty and appropriate, so, those we are comfortable with buying. Not anything that is inappropriate in terms of slogans, patterns, etc for a young lady.
For comps, well, ummm ... yeah. Commando to avoid any problems.. Let's leave it at that