Ok bit of history first. I have a neighbor. I dont know them very very well but I like her [her DH i am still uncertain about]. She has a son who is the same age as my DS4. The kids are not close friends mostly they coexist on their playdates. Now I mentioned last month that we r going to Disney to NDH [neighbors DH] in the passing. Now NDH is leaving to scale Mount Everest 2 days after we leave. He will be gone a month. So NDH asked me if its ok for DN and her son to join us. The way it was put left me no choice to say yes. After all what could I have done if they had come without asking. Anyways they book POP and everything the same as me. I gave them the required info and all. Till here its fine. She is not very particular about ADR's [clueless is more like it] and has told me she will go with whatever I decide. I told her about the ADRS I made and gave her the link to each menu. I sent her a generic packing list too about things we need to take. NOW here is my problem she is not taking any of the planning stuff seriously. She told me yest why will i need ponchos in May? it wont rain then!. Fine by me but if it does how will i let another kid my sons age get wet when i am dry and cozy?? Then comes the problem with Tshirts. My family is gonna coordinate our shirts. I am getting graphic designed and I will print them. Should I tell her about it or just keep quiet? Will it cause a issue later on? Similarly; though I told her I am gonna buy glo sticks before i leave she is not doing it. I really dont want her child to end up using our stuff. I am not being selfish but I will be carrying limited stuff.
I am not sure how to handle this without causing any bad feelings. I like her and wanna be friends with her but I dont know how to clear the air on this? Also I dont want to be paying our of pocket for her expenses as we r on a tight budget too.
I am not sure how to handle this without causing any bad feelings. I like her and wanna be friends with her but I dont know how to clear the air on this? Also I dont want to be paying our of pocket for her expenses as we r on a tight budget too.

I'm a little unclear as to what your role is supposed to be here. It's one thing to let them essentially barge in on your family vacation time, it's another for you to act as tour guide/babysitter/day planner for them. I can't imagine what gives them the idea that you should -- but regardless, it just isn't something I would get into because 1) resentment is inevitable (you already sound resentful IMO and rightfully so, and 2) it's just plain not your responsibility to make sure they have a good time. It sounds like you've already shared some of your knowledge with her and she's choosing to disregard it. So be it, but don't feel guilty about it or feel forced into doing her job for her. As for paying any of their expenses.... I can't even go there without risking getting banned from this board.
There is so much on the line. Everybody wants to have the "perfect" vacation and that means different things to different people. 
Wow...that was SOME position your neighbor put you in. I think I would have been caught off guard with the request, and probably said yes too (although kicking myself inside as I said it).
I mean it's not like you were going camping for a week or something, these things are expensive!
) I would ask your neighbor what she thinks of this whole situation. It could be that she is totally uncomfortable about horning in on your vacation and that is why she says she'll just go along with whatever you have planned. I think if she wants to be included in your dinners or whatever, that would be okay so she doesn't have to eat alone, but really - spending the whole day with them? She'll be in all your pictures and everything? Years after they aren't your neighbor anymore, you will look through the family album and there your neighbors kid will be in all the family pictures at Disney!!

(really nothing to what you have to do now. My DH & my DFriends said say it's a "family vacation". I think that I have gotten away from problem, hasn't said anything
Good luck with your ISSUE!!