With my new heroine I find it hard to defeat Alduin, explanation, she is a vampire!
When I first got to the quest I think she was a little bit low leveled and didn't have enough skills. I also didn't have so many weapons with me so I left it for a while. Then Dawnguard came along and when it was time to choose, I accepted "the gift" for fun.
Now after gaining in skills, better weapons and higher level I tried again but failed. She can't harm him at all. Big sigh.... It wasn't that hard the first time I did this with my other heroine, Dahlia!