Bell, there is no reason to wait. Actually, it is advisable not to wait at all. Disassemble the phone using this guide. Clean the iPhone using this guide. It was written for a 3G but it is the same procedure for your phone. This will also give you a chance to inspect the stuck buttons. The cleaning might even free those up. It is important to clean it properly so as to avoid any corrosion damage that potential will put an end to the phone. Once it is cleaned, replace the battery. Re-evaluate and see what damage, if any, you really have. Yes, if the charging problem persist, I would change the dock connector. Hope this helps, good luck.

Have you let it dry? As you surely have heard by now, don't turn it on! wait at least 3 days with your cell phone open.

The same thing happened to me 3 weeks ago and it's working again.

If it does turn on after 3 days but it doesn't charge, it might be your battery, that's what happened to me. To check if it indeed is the battery you have to download the iPhone Configuration Utility, available directly from Apple in their website. Check the error log and look for battery errors.

When I took it to the repair center they assured me that the problem was with the dock connector, so I would try that also if I were you.

Try to test the parts before you buy them!

Hope this helps, I went through the same as your sister, but Don't Panic!.