Perhaps you haven't explained the rule about safety, and the consequences, clearly enough. The reason for safety equipment while using ANY form of transportation (seatbelts in cars, helmets while on bikes, rollerblades or scooters), etc, should not necessarily be "because I got hurt". That really doesn't make much of an impact on teens, who often think they're smarter/quicker/better than their parents at pretty much anything. Of course, a parent who suffered an injury as a child or teen can often add a personal note to the rule, but that's not the whole story.
Instead, you should sit down with your daughter and explain that safety is important, in and of itself. In a couple of years, she'll be old enough for a learner's permit, and you (hopefully) will require that she wear seatbelts, doesn't drive distracted, never texts while driving, etc. But now, her mode of transportation is skates. And while on skates, on any surface, a smart and careful person wears a helmet. It doesn't mean the skater is not skilled. It means there are careless drivers out there who strike innocent victims, it means a skater can encounter a pothole, a kitten that runs out in front of her, a gust of wind, a child, etc, and can lose her balance. And the head will go down hard.
Your focus is off. You're letting her brain and skull go totally unprotected (and believe me, they're a lot harder to repair than a wrist), and you're insisting on wrist guards because you broke your wrist, and you give in rather than insist on a clearly communicated rule. Will you give in when she's driving, and let her text, and let her pile 6 girl friends in her car, sitting on each other's laps without seatbelts? I mean, giving in would be easier, right? She got to school, right? I hope you see the connection.
If she has to go to school, which of course she does, and if she takes off on rollerblades without a helmet, or borrows a friend's skates after you've confiscated hers, you drive her to school, which is WAY less cool. And you ground her and make her stay at home doing chores if she won't obey a simple safety rule.
But you make the rule clear, you tell her you've been slacking off from enforcing a rule, you establish the consequences, and then you FOLLOW THROUGH on your word. Or else you're going to end up with an injured child, or a careless driver, and a teen who knows that you'll just give in. Don't make the rule about your past incidents. Make it about your child's future.