On the one hand we have all seen folks ferry folks on the back of bikes like that. And the extracycle seems designed for heavy use.
On the other hand a lot of tubing charts top out at 180 pounds, and you can go heavier, but if you weigh the same as her you are at 270 from the get go. And the weight is biased towards the back end, and possibly one side. Also a few (as many as I have been able to get to) long range tourist coment the one bad undersize thing on a touring bikes are the rack mounts which are basically fender mounts. A lot of folks get breakages. There isn't any real rating on the cast parts, and they often aren't all that evenly formed. So it is hard to feel that confident.
Recently the FF guys have been reaming on us backyard guys for not having 35 year experience to back up our projects. An example of something like that here would be BMX pegs, maybe not 35 years, but it's a big market. I once studied a series of fancy front forks they use for those bikes, and was impressed with the titanic way they mount some of the those threaded load take-off. Very beefy. So that might be the kind of thing to study. I was just looking for ideas for ultimate touring racks, and there the loads are probably at most 60 pounds.