Judicious and well-deployed telling is an underrated skill in modern American story-telling! You don't even have to go back to the ancient Greeks: Jane Austen uses it to great effect. It helps if there's a sense of a personality telling us these things: the Nurse in Medea, or Jane Austen's ironic narrator. Telling can be very engaging as long as there's some emotional impetus behind it!

Yes, I'm sure the nurse is well aware of what Medea would do to anyone who tried to cross her plans, and also well aware that she probably wouldn't manage to save the boys anyway (say what you will about Medea, but she finishes what she starts!), so she's not getting in the way of another poisoned dress. Maybe now that Medea's leaving Corinth, the nurse will finally get a new boss?