I don't think we used a specific packing list for someone for a child of DD's age (she was a young 3 when we went in Sept). We just used one of the generic packing lists on the web for Disney that was at the top of the google search.
I did opt to use pull-ups instead of underwear in the parks. While DD has been solidly potty trained for 6 months, we did not want the preassure of being in long lines, looking for bathrooms, and having accidents. The good news is that she made it through the entire trip without an accident, but the piece of mind for me by having her in pull-ups was worth it.
I also would not bring life jackets for swimming, as the resort pools on property have them there if you are staying on property.
If your daughter is into princesses, maybe bring a few dresses. I brought two for my daughter and she asked to wear one after seeing a few girls wearing theirs at the magic kingdom.
if you are driving, a step stool for using the hotel sink would be great. We flew so I could not bring that and I just pick her up to wash her hands and to rinse for brushing her teeth.
My DD has been trained for 8 months and I have a 5 year old with me. She is wearing underwear. We have just been careful about potty breaks before getting into lines. Just couple of hours or after a meal, DH and I will say we have to go potty and then we have the kids go too. We have been here most of the week and so far this plan is working great. We have not had anyone have to go while in line.
Kids are just becoming potty trained so we will have to bring pull ups. Also debating purchasing a fold up collapsible seat for them also.