idea #1: Have her husband piggyback everything she's doing and just change the date to be a week earlier so she gets EXACTLY what she wants and chose herself, but it happens early.
idea #2: Do it in a place that holds sentimental value for you guys so that even if the quality isn't awesome it doesn't break the bank and you know she'll love it and understand the choice because of the memories she shared there with her friends.
idea #3: Have it outside or at a house or get a space rental and select guests to each host tables. Each table can have a hostess and each hostess will furnish their table with silverware and plates etc. The food can be potluck and everyone brings something which will be part of the gift-- home cooking-- and she will be sure to find something amongst the big variety that she will like. Put an extra seat at each table so she can sit wherever she wants and float around to be wth all her guests.
idea #4: Don't make food the center of attention; hire a band and have dancing or something, or go out somewhere else and let her decide on the fly where you all go to eat afterwards.
Last thing: I hate surprise parties and would NEVER want one for myself because I, like your friend, am a control freak and if my name is attached to something I want it to be my way. Plus I want things to be convenient for me and I want to know to be in party-spirits when the time arrives and dressed well etc. But if she has actually TOLD you she wants a surprise party, she must understand that it is not going to be copybook perfectly the way SHE'D do it-- how could it be-- so she must understand that you'll do your best to make it a gift from YOU to her and it will be done kind of YOUR way as well as hers. If she has asked you for a surprise party and she never got one before, you cna't go wrong so long as you're trying. You're the first person to ever do this for her and she's gonna know you did your best and with all her friends there to celebrate for her, it will be meaningful and she'll love it even if it's not perfect.