Damien I mean, on the one hand you let her do the one thing a chastity belt is supposed to prevent, and it is fair to see that as a keyholding failure. Safeword use should immediately be followed up with a conversation about boundaries and why the safeword was used, and you did not have that.
On the other hand, you probably did not have an unlock procedure in place, and in that case it was the right call to end the no-longer-consensual arrangement as quickly as possible. Give her access to the key first, talk later - the safeword means she no longer consents. The fact that she decided to violate her chastity before talking to you is on her. Being her strength against safeword misuse only becomes your responsibility if you have (consensually) defined a safeword procedure that does not start with an immediate unlock.