I don't usually take time arguing over webtoons with strangers but lol. I agree with you that with what she has been through, its a proper reaction. But you're only looking at one side. You should consider her friendship with Allendis as well. He is her first friend, and instead of considering that Allendis is too practical and obviously won't believe her the first time she tells him, she instantly goes BETRAYAL. Also, if he was the type to just believe her instantly, that would make him a too naive character (and we know that's not what he is).
And with that, I'd like to repeat once again that she overreacted but she also could have not but where's the drama in that?? In the end, we're all just reading a story underneath the drama genre anyway ¯_(ツ)_/¯
Idk if its just me but I think she overreacted lol