Actually it says you'll be billed for a "Member Credit", which "can be redeemed for any JustFab style on the site".
I'm not sure what that means exactly, but if you can actually redeem one of those credits for $39.95 worth of product, then 1. it's still very misleading because you spent a lot more money in their store, on their products than you intended to, but 2. at least your money didn't just evaporate, except 3. is there anything preventing them from at some point deciding "From now on, we will only sell novelty dish-washing sponges, at the great rate of one credit per sponge!", making all out-standing credits worthless in a single TOS change?
The grandparent's link says "Each credit can be redeemed for any JustFab style on the site."
Seems to me that they're saying if you're a member but didn't make your decision for your free (sunk cost) product by the 6th, they charge you and turn it into store credit. It's not like they're charging you and saying "too bad, you don't get anything."
It may be different, yes, and I can relate to the OP's original complaint from his girlfriend. Still, given the language used on the site and the (albeit weird) use of a "credit" that can be used in the future for each month you don't buy something, it doesn't seem unfair at all to me.
I will say that the negative attention this confusion could bring them is more harmful to them than if they revamped the purchase process to just make it crystal clear what you're buying.
From my experience at Poll Everywhere, the "sidebar" on the checkout process does not get read by anyone, anytime. For some reason, the sidebar becomes a blindspot and is ignored (at least in our testing) during a checkout process and so is thus not a great spot to put reminders about how you're joining a membership and will be charged monthly if that is the only place is is put.