Scene? 100%. Over. You need to have a conversation anyways so it's hard redlined. Even if you are feeling fine from it, it has to be understood that you may not have been. I've found myself pushed over lines I really felt uncomfortable about and it caused me slight consternation, and I am extremely mentally healthy.
Relationship/dynamic? It is absolutely up to you. For Amanda, she's willing to take that on. For Dawn, she isn't. Neither is wrong, per se, in my opinion. But you should feel no duty whatsoever to continue. It is absolutely within your discretion. And I agree that one maximum is the only reasonable limit. Anything beyond that and it's not really a red line.
Remember: Boundaries are about fairness for everyone. It's not just for you, it's for them too.