IChat video connection issue, not related to router

Question

I received a brand new 20" iMac Core 2 Duo just yesterday and intended to use iChat AV to video conference with my girlfriend, who has a 12" iBook G4 1.2GHz with an iSight and all system software up-to-date.
We both have DSL connections at home. We also both have wireless routers. The very first time we tried a video conference, it worked perfectly without a hiccup and everything just looked and sounded wonderful. At the time, she was connected wirelessly and I was connected both wirelessly and through Ethernet to my router's local network.
The second time we tried it (only a few hours later), seemingly without having changed any settings, it failed to work, and hasn't worked since. At first, we would get Error -22, saying something about how bandwidth is insufficient to maintain a video conference. However, I do not believe bandwidth is the real issue since all other network/internet tasks on both ends are spiffy as usual. We also both tried turning off Airport and just connecting through Ethernet to our routers' local network. Same problem.
To then determine if the problem was with one our routers, we both set them aside and plugged our DSL modems directly into our computers and connected to the internet with PPPoE. This appears to partially fix the problem: we are able to initiate a video conference, we both have audio, I can see her, but she can't see me; sort of a one-sided conference. On my screen, the image of myself freezes as soon as the conference is initiated. So unless I'm missing something, the ultimate cause of this problem doesn't appear to be the routers.
You can bet I tried a bunch of the common tips mentioned in this discussion forum before posting this question, such as changing the iChat port in the preferences, turning off Firewalls in the Sharing preferences and changing Quicktime streaming speed.
In summary, it worked once and hasn't worked since, and routers do not appear to be the cause of the issue. Does anyone have any further advice for me? Any help would be greatly appreciated! Thanks.
iMac 20" Intel Core 2 Duo 2.16GHz   Mac OS X (10.4.7)  

Answer 1

First off I want to thank James for his willingness to help me test connections today. James has suggested I check into upping my Mother's connection. I will definitely look into that.
I wanted to update the thread that I tried the three test accounts at Apple (appleu3test01-3) and had success from all three on my home computer via my wireless configuration no less. This is what stumps me about my connection issues with my Mother - we can both connect to others but between us we get error -8's since iChat 3. I also find it odd that this is happening even though we are both Earthlink customers - I would chalk it up to routing tables or something if we were on different ISP's.