Hm, so she didn't just use the facts that this kind of flower and incense together are poisonous, because she was afraid the aunt will play ignorant and say she didn't know (because it is not common knowledge) ?
So it was best to seem still naive to them, by saying the mother is allergic to flowers?
This is then really like gambling, betting she will get out of their next scheme with hopefully more/better evidence than now ...
Thank you for the update!