IP Address forwarding for Minecraft [Bukkit]?

I'm trying to either host or play on a Minecraft Bukkit server with my sister and neither of us can get our Minecraft servers to work.
I tried everything I could think of, I did the 'raw' download of the server files from the Minecraft.net website, I did Forum tutorials, and I even tried an automatic-setup-bukkit server program and so far, I've only have 1 positive result.

I'm no idiot, and I'm not technologically challenged, my port, 25565, for Minecraft is open, the server is running, and I've even connected to it locally with my own (wireless) 192.168.XXX.XXX:25565 IP, and by the TRUE IP, 24.240.XXX.XXX:25565 and I've jonied it, but when my sister tries, she gets a time-out error every time.
I disconnected the ethernet cable between my modem and my wireless router and connected straight into the internet connection coming directly from my ISP giving my computer the same local and true IP, bypassing my, and therefore not broadcasting, wi-fi, which every laptop, phone, and other computer is connected to, as well as the phone system we have, and my sister was able to join by connecting with the ip 24:240.XXX.XXX:25565.
However, I can't possible disallow everything in the house access to the internet just to host a Minecraft server on my laptop as well as she the fact that she wants to host the server so she can keep the most recent world files on her computer, since it started off as her world in the first place.

The ISSUE that I believe we're having is that the modem and the router aren't communicating correctly and that when I try to connect to her server, my Minecraft game IS making it to her MODEM, but it doesn't know how, or won't, sent my computer to hers to connect to the server due to it giving her a local, 10.0.XXX.XXX, ip address.

The QUESTION(finally) is /how/ do I get her modem-router(they're the same device, unlike at my house) to forward my Minecraft game to her computer so it can connect to her server?

You can't you need to be careful of the computers that are just not meant for gaming. Do research and find the right one for you.