Hi Gilda!
Probably the biggest difference between Standard Dining and Quick Service is Standard Dining comes with at least 1 table service each night. If you and your daughter would like to experience one of the character meals (which are all table service), than I would go with the Standard Dining Plan option. Or perhaps you'd like to relax and be served vs. serving yourself, and that's some of the advantage of a table service.
Probably one of the biggest benefits of the character meals is the fact that they come up to you to take pictures vs. you having to seek them out, or wait in line at the Park's various Meet and Greets. My daughter, who's also 6, really enjoyed this part of the deal (smile)...
But if table service/character meals aren't really your thing, then I'd just go with the quick service. It's less expensive, plus you don't have to worry about making reservations. I should note, however, that many quick service meals offer very healthy portions, in case you're thinking about how much food your daughter would eat.
You save 20% choosing Quick Service, and 30% choosing Standard Dining, this is all compared to paying out of pocket.
Each Plan has benefits, so it all comes down to preference.
May you and your princess have a magical time on your Disney vacation!