Veggie Friendly Monterey Park/San Gabriel
Have you had a read through this thread?
How strict are the vegetarian(s) in the party? Eating at pretty much any Chinese restaurant that's not entirely vegetarian always carries some risk of getting some sort of animal product (chicken boullion (ji jing), chicken or meat stock, oyster sauce, non-vegetarian shacha sauce, etc.). I know these risks and eat at non-veg places all the time anyway, but even if you ask all the right questions, there's always some risk. All that said, I think Mei Long Zhen would qualify, and it's fairly nice. The bigger Shanghai place in Focus plaza (second floor in the middle) is also fairly nice, or at least not hole in the wall. Elite (banquet place) will do vegetarian stuff, though it's mostly on the bland side... might be a good choice for this occasion, though.
I am starting to sound like a broken record, but the new Loving Hut in Alhambra, while smaller than other outlets of this chain, is clean, light and airy and has good food. I had a vegetarian mongolian "beef" that totally blew my mind.
Desserts are uniformly horrible here though. Go elsewhere. Fosselman's is down the street, btw.