I too, have heard of people doing this but me not having any expierience with this doesn't help. My guinea has been fine with veggies always and loves them. I think it may be a good idea to first wash the lettuce and while it is damp sprinkle it on. I generally don't think vitamin C tabs or vitamin tabs are necessary but I guess it is alright as your pigger doesn't like any veggies. Here are a few helpful links:
http://www.guineapigcages.com/forum/...ang-water.html http://www.guineapigcages.com/forum/...arts-info.html
Maybe you should attempt to try some other veggies?