It's not like I don't get why Piper didn't tell Red about the bakery. Obviously it was to spare Red's feelings (and no one I've seen has called Piper a "Stupid b@#%#!!!" or anything else along those lines). But it was still a dumb move on Piper's part, both for her sake and Red's.
Red is going to find out eventually -it could be tomorrow for all Piper knows- and how's Red going to feel when that happens? She's got her head in the clouds imagining the bakery is doing all well and good, only to find out the entire thing is a fiction -now she is doubly crushed. On top of that, when Red finds out (not if) how does Piper think she'll react? It won't be thanking Piper for lying to her, that's for sure.
As far as Piper is concerned, it was short sighted and, as I said, a jerk move -because Red will inevitably find out sooner or later.