Heather’s not familiar with the running gag.

↓ Transcript
Early on in plotting things out, as far back as when I introduced the Fairweathers even, I considered the possibility of having Barb turn out to be Todd's biological sister.

I discarded this idea a long while ago for a variety of reasons, the big one being a bit of a tipping-point on the coincidence/believability meter.

In fact, I decided to use this tidbit for the Commentary just to get the idea out of my head and make it stop trying to convince me to use it. XD