Poor hubby. He does something nice, and really not so irresponsible, and you're cross at him because something happened. If he applied the sunscreen, he did a great job. Cut the guy a break, and try to remember that your kids are going to go out in the middle of the day sometimes.
Let's face it, no matter how careful you are, your child is bound to get a sunburn at some point. It's a fact of life. And skin cancer is a problem - a big problem that you can't really escape. Not only for those who burn at a young age, but for all of us. Her burn is no guarantee that she will have melanoma later - and keep in mind that just because your other daughter didn't burn doesn't mean she is safe, either. Non-UPF clothing runs about SPF 5, but very few people think to put sunscreen on under their kids' clothes before a trip to the park or the zoo, for example. I'm not telling you this to stress you out. Instead of stressing about something you cannot change, relax and figure if it didn't happen now, it would happen later. Teach your children (and husband) how to put on sunscreen regularly (no matter the SPF rating, sunscreen should be reapplied at least once an hour), and also teach them how to check their bodies for melanoma. These are both skills that they'll need as teens and adults, and so instead being mad at your husband, consider this a great lesson for all involved.