Do you know the novel where the female protagonist was reborn in a girl who has butterfly poison on her face (I think) that saves a prince that was plotted by his fiancée to get to his brother to be empress? The original owner of the body was slowly poisoned.
She was a poison tester who was granted the right to marry and then her son gave her a fruit (which is the reason for her being reborn).
The guy pretends to have amnesia when he returned because he was victim of a plot by his fiancée.
The girl also eats all kinds of poisons and then it produces tattoos on her body which she can summon.