Rhiannon Erica Kerrigan:
What are the rest of us doing?
What do you want to be doing?
Cathal has twice left it open for the other PCs to do things, Sarah has done some things, the second of which she is currently engaged in.
In the absence of any other actions I made the executive decision that Charlie would do something, which primarily revolves around finding out exactly what is going on, since I and therefore she, had expected that Cathal would find out what was on the other side of the tunnel and report back, before moving on.
I have no problem with the fact that he chose not to and go find out things himself, as that action is perfectly valid, it just means that things have to unfold in a different way.
Part of that now requires Cathal's input, in response to Kasamir's warning, which will likely occur when he comes online later today (it being early am Thursday as I write this), before things unfold further, including an actual report of what lies ahead by Kasamir (literally your eyes-in-the-sky).
Charlie needed Kasamir, as he's the best placed to give her the overview she needs, and Kenneth being almost the most combat orientated of the characters, as the most logical escort. She's also somewhat aware of what his 'rifle' brings to the party. Given she hadn't any more idea of what was ahead than any of the rest of you, she wasn't going to take more than the minimum people she needed to to find out.
If Rhiannon really wants to tag along then in reality Charlie can't stop her, in the same way she can't stop Lord Kylestenson, who has his own motivations in regard to what is happening.