I'm going to cancel lunch with an old friend shortly
Why cancel on the last minute?
I'm not sure if I like the food in that restaurant.
Instead of cancelling I think that you should just suggest another restaurant. If you cancel last minute you might really upset her.
If the food sucks. Now I'm going to piss her off.
No one will get mad about bad food. People just chuck it up for experience and never go back to that restaurant in the future.