The only thing surprising about this reveal is that she is a bit bustier than Angelica. This was probably way more surprising in novel form.
Don't make the character look like a girl if you're trying to make it surprising that she's not a boy....now if she turned out to really be a boy that would have been surprising.
Okay, I looked up the web novel (cry, how could you make me read just straight Japanese, no pictures!?). And basically, the relevant section is like "And thus entered the 4th person that would be staying in the room, and for a moment nobody could believe their eyes. "A- a woman?" Rick muttered to himself without thinking."
Which is to say, even in the WN, they were immediately like "Dude looks like a lady"