Definitely have a discussion with her about it, because there is no way that you should be paying that much. For one, that is the majority of your wage going straight to her, rather than on progressing your life. If she feels as though you have to pay that much to cover bills etc then suggest she goes on a comparison site, because if you're splitting the bill then that's an horrific amount each month. Otherwise, she is getting you to pay the majority of the bill, so she has a nice cosy amount of money tucked away for herself.
I currently pay £100 every payday, and that covers travel to and from work, contribution to the bills and for food. Even then some would consider that a lot.
You need to be up front about it and say you do not agree to pay that much money anymore, how are you meant to save up for things when a good chunk of your wage goes towards board & then the rest to essentials (and alright some not-so essential stuff)?
For me, board is meant to help alleviate how much bills cost the household (individually), so find out how much she is currently paying, and come to an agreement over a smaller contribution fee.
Perhaps discuss with her how much cheaper it would be if you paid for your own food? You may find you'll make a saving even though you do have to pay for your food. There are plenty of cheap supermarkets out there, where you can get great quality food for a relatively low price.