It is sooooo tempting to have the next comic just be Mrs. Dunkel briefly returning to grab something she forgot and then immediately going back out again, but spoiler warning, that’s probably not what’s going to happen.
Depending on the number of available rooms in a home, the number of people living there, yadda yadda yadda, I could see it being totally understandable for a brother and sister to share a room even in their late teens. If the space is available, however, I’m pretty sure the vast majority would prefer separate rooms, and the Dunkel house has the space for it.
Granted, they'd have to give up a room for it, and one of those rooms is where Elliot and Susan do their review show, so no. Elliot and Ellen will just have to share until one or both of them move out.
Incidentally, Ashley’s next word in panel five would have been “deterrent”, or something meaning the same thing, anyway.