This lady's name is Donna Vivino. She was the UNDERSTUDY for Elphaba in the musical Wicked.
Jackie Burns was originally cast as Elphaba but sadly had to miss her last performance due to a case of viral laryngitis.
This is a perfect example as to why when people say "understudy's aren't as good as the original" you have my full permission to punch them directly in the face. I have seen a ton of wonderful understudy's and let me tell you, all of them were FANTASTIC. Not once have I ever seen an understudy and thought "Oh I bet the originally casted person does way better than this guy!" Never have I thought that. When I saw The Lion King Scar had an understudy that day and he was absolutely wonderful. At a somewhat local theatre production the character of Annie had an understudy perform for her in Annie. And she rocked.
Basically don't diss understudies because if you do you are a moron and will look extremely foolish when said understudy who has put up with so much crap from the other actors/stage crew/directors takes the stage and outshines the male or female who is listed in the programme as that character.