You're assuming that the folks saying "we'd like to get together another time" are expecting YOU to organize that! They are not. The effort is up to them now -- if they say "we'd like to see her" they they, not you, are the ones to arrange it. Focus on your one party and then next time you talk to them, just say, "Whenever you'd like to see Daughter and us just let us know what you have in mind."
It's very, very typical that some folks just cannot make a specific date and time and it's also nice that they mentioned doing something else. But you are not expected to arrange and provide some alternative "event" for them and your daughter. I'm sure the folks who said this to you did not mean to make you think you had to create multiple new events for all of them. Remember-- they, not you, made suggestions about the park or the zoo; so just mention when you talk to them, hey, if you still want to meet at the zoo or whatever, let me know what your plans are.
Don't add to your stress over the party by thinking you are now expected to create more parties in other locations.