If she has a sponge filter, you would put the whole thing in the tank, and let that work on your tank, while also running the AquaClear.
Also, since you do have an aquaclear, I would recommend cutting the sponge in half lengthwise like this |----| and just use half the sponge, and buy more of that biomax stuff to put in the filter, especially since you have two goldfish in there. If you want me to explain the reasoning behind this, just ask and I can clarify. Or you could just take my word for it (it's what I do, and everyone else I know that runs AC's.)
You may also ask her if she has some biomedia you can borrow. I got some lava rocks, and a few of the biomax things from some people I know, and put that into the filter inside the mesh that comes with the filter. That may be easier for you to do, instead of asking for a sponge filter.