The route grade guidance for Girls Youth B is 6b - 7b (approx). But remember that the routes will start relatively easy ad not get to those grades until after half way. The Boulders will be approx V3 to V5 / V6.
In reply to LettieT:
Give it a go. Generally girls B is not a huge group.
But good to climb with people your age and if its your first comp will give you an idea on of what you can work on. Its a fun low pressure comp.
The beauty of the Youth Climbing Series as an entry level competition is that every hold you reach accrues extra points so everyone goes away feeling like they have achieved something. Plus you can compare your personal score from round to round.
The kids are generally great and will look after the newbies so a good way to make some Climbing friends too.