If I remember, canceling Embrace cast will still use the GCD. This means you have 2 choices : let her finish her auto Embrace and then ask her to Embrace or interrupt her and then still wait as if she had casted it and then ask her to Embrace (quite useless).
I was happy when I heard about the Heel/Steady mode but this is only effective on Whispering Dawn because it's a non GCD and after interrupting Embrace you indeed can cast Whispering Dawn. But interrupting Embrace you can't cast another Embrace right away cause the GCD is lost at the second she begins to cast Embrace, you will still need to wait the whole GCD, so better let her finish her first Embrace anyway.