When I see first time planners they all tend to make the same mistakes, over and over again.
These are just a couple of questions that should be answered before you move forward.
- Why on earth does it have to be at a restaurant? Why can you not do it at someone's house to save on costs?
- Why do you need multiple showers? Can you not invite all guests to one shower? (If there are too many people, I can see why you'd need to host it at a restaurant, but I don't understand why you would need three showers.)
- Your sister should give you a guest list and contact info for those people, that way you do not decide who to invite.
- If your sister's friends seem to think it has to be adorable because they are event planners, let them host it and pay for it. Or ask them for cheap and cute ideas that you can afford.
- For favors, there are a million ideas out there; bath bombs, nail polish, alcohol, etc. Depends on your theme and the feel you're going for.
First off restaurant showers are way more expensive. Generally the host is expected to pay the entire restaurant tab. I have never been at a shower where the bill was split among guests. This is why events are usually hosted at someone's house or a hall where food can be made. One can save by having the shower in the early afternoon (1ish) and just serving some appetizers and cake. Showers are usually at someone's house and the hosts provide light food and drinks. It can even just be cake and punch as long as it's not directly over a meal time.
And no, she can just invite people she is personally close too. There's no rule that says XYZ has to be invited.
Why are you having 2 showers? This is something that young hostesses tend to over due. A shower is a shower. You have one of them and then you call your work done. Could you imagine going through all of through work of planning two guest lists? It is almost all that we can do to plan and invite one set of guests. Organizing two parties is trial by fire at best. The chance that one of them will be a success is low when you heap another one on the side.