find out who's doing her PR
, contact them asking if you could have a photo pass. sometimes they're nice, sometimes not. if you don't work for a professional organisation or freelance for something specific (ie a magazine) OR are vaguely known for your photography, it's pretty unlikely that they will give you a photo pass, but it's always worth trying.
bear in mind that most photo passes usually, depending on the gig, only allow you to stay in the photo pit for the first say, 5 songs or whatever, anyway.