I am going to go in contrast with most everyone here.
How does it fit your head? THAT is the most important thing. There are lots of good makers with similar quality. Bell, Impact, Simpson, Pyrotect, G-force, and some others I have seen around. Find what fits best. I would lean tward a full face helmet. Lots of the older certs are floating around on brand new helmets that make it so you can get a great hat for almost half the $$. Check ebay. For her, a current cert will not be the most important thing. Find out what fits. My head fits Bell. I cannot wear a Simpson no matter how good the quality is. Just cannot do it. So I wear what works.
For me, I would not rent. Get one that works and let her sticker and doll it up to customize it.
If she were racing funny-car, I would worry about the best one out there. But for a 14 second car, get a decent one that fits well.