Hi, my friend thinks she is dead set on trying the big Texan challenge but she is allergic to shrimp so can they substitute the shrimp for something else?

Yes

I'm sure they will hook you up with something else same weight, good luck!

I'm sure they'd be able to work something out. More salad,additional roll etc.

Yes they will accommodate you

You know i honestly don't know. I'm sure they would be accommodating. Tell her to just start on the steak. I've only seen one person attempt it and he only ate half the steak...nothing else! Maybe call ahead and ask about her allergies?