First Note: You've convinced me that I REALLY need to learn post-processing on the PC... of course, I really need a DSLR too... *sigh*...
Second Note: I hope you're willing to take suggestions here
... On the picture of Larissa in the blue-shirt where you were concerned about the "pure-white" Do you know what you were metering off of? If you were metering off of a dark color (i.e. the leaf) that would tend to give you the pure-white also. When taking a shot, particularly in the bright sunlight, I always try to make sure I'm metering off of a medium color (i.e. her shirt) when I can in order to bring out the biggest range of colors.