A bit better? But I'd still go with "duże śniadanie".
Because "śniadanie" is a specific meal. It's hard to talk about the amount of it, but you can eat about the 'size' of the meal. "Zjadłam dużo jedzenia" is perfectly fine, "Zjadłam dużo ryżu/zupy/mięsa/ziemniaków" etc. as well, but here... I don't think so.