Okay, I have to say at princess parties but she's your baby and girlie stuff is somewhat inescapable I hear
Suggestions.
Set out hat templates, crowns and pirate hats, for toddlers to decorate, using stickers and felt pens - have a roll or two of selotape nearby for adults to stick them together.
You could also have a treasure hunt for gold coins (pirates booty)
Buy some brightly coloured plastic plates, you'll end up using them time and time again so definitely worth the investment. You can get cheap primary coloured ones that suit picnics and other future parties.
Invitations. Depending on size of party, you could get dd to do them, you could print out pictures of pirates and princesses and get her to make a collage affair on A5 paper and write on back. Or you could print off a photo of your dd and stick/draw princess crowns and skull and crossbones as boarder on back where you can write party info.
Party bags. Again you can buy these blank and decorate at party but personally think you would have too much craft stuff going on then so save this idea for next year. Instead you could use something like a treasure box
Include these La fruit and more gold coins, and one or maybe two other things (small things! necklace/watch notebook)
Are you sorted for food ideas? Will parents be staying? How many are you having?