That ridiculous sword just takes me threw half my hp and shes ridiculously fast...

... there's also her ability that lets her regen her HP.

I'm guessing that you have to use others to kill Umbra, i.e. legion of guards because others aren't affected by 100% difficulty, only you.

She would probably destroy them but you have gave me and idea...do you think she would follow me in the oblivion gate?