I believe I do have a timeline of events that you might find elucidative.
Deborah arrives late to give a fencing lesson. She easily fends off her student while giving him instructions, despite the fact that she hasn’t yet had time to change out of her heels.
During the lesson, she deduces that her student’s partner is away at the moment. This comes from her observation that he has his phone in his shirt pocket, which is what he does when his mother is babysitting.