Gear Nazi!!
Children, now simmer down...
Here's my take on it (my opinion/interpretation):
Sasch, you're imposing your own gear rules (what you think you should wear) based on how you plan on riding during a group ride, expecting she's going to ride at the same level regardless of what she's wearing.
From the sounds of it, if she actually were to show up for a group ride wearing only jeans and a t-shirt, she has the common sense to ride at a much more moderate/conservative pace. My advice if this happens, don't let her ride point so you won't get frustrated riding behind her at her pace.
I just hope that common sense prevails when we do decide to get geared up for a group ride, and that, regardless of when or where, nobody has to find out the hard way about pain & discomfort that gear could've prevented.
Now play nice so I don't have to put you in the corner for a time-out!