Tipping at a catering hall for bday party

My aunt is throwing a surprise 30th bday party for my cousin at a catering hall. The price includes 20% gratuity. Is she still supposed to tip extra? There will be 2 waiters, a maitre D, a bartender, and some coordinator lady. Its a sunday brunch.

I know they expect it at weddings but what about for a bday party????

TIA: