To be honest... I'm not quite sure, because I never use the default Linksys firmware. If you were running DD-WRT I could help in a heartbeat. How did the gf get it connected to her network?
Is the STB pingable from inside your network even when DishRemote is having issues? If so, then it is a problem with DishRemote, not your network. I have found DishRemote can be very flaky at times. One of my 722k's works just fine almost every time, but the other always has "connection" problems that I have figured out are not caused by my network. I found that while being in DishRemote, clicking "My Account" in the top-right corner, which takes you back to your account overview, then clicking Dish Remote Access again, usually fixes the "connection" problems. If it doesn't work the first time, try it again.
Another thing to check, in the top-left menu on DishRemote, where it lists your receiver(s), there is a little dot that is either green, yellow, or gray. If it is green, of course that means connection is established, if it is yellow, I'm pretty sure it's safe to assume that it is connected to your network, but DishRemote itself is having issues. If it is gray, then your STB is not connected to the Internet.