Responses
From previous chapters you could see that she would always Light some up for him (and the empress when she would come in would say how she hates the sell etc.) so it was a daily routine... Plus she is acting like a fragile white lotus in frond of others so I bet they wouldn't excpect her to have the guts to do smth like this...
That's true, but a common scenario in such a stories is gradual poisoning in small doses. Regardless, it seems like this detail was deemed insignificant to the upcoming events which might be why it was passed by like this.
How come the crown princess is not even a suspect when she said she light up an incense for him the prior night? Especially when he was suspcted to have died from smelling poison.