But i think she already drink the tea???

The tea we saw earlier in the scene was the correct tea that was not poisoned but as soon as the little boy came and she got the second one that tea was poisoned. the one she was going to drink with her son was really suspicious because she got one prior and then immediately as her son came she got tea again so from we can assume it's that the second one was poisoned and not the first because the first was the correct one

Thank you so much.

(=・ω・=)