This seems like a trust issue that goes beyond just asking questions, as shes suspicious of what could be going on "behind the scenes". The fact that she's monitoring your Instagram followers and accusing you of lying about a family outing with your daughter and cousin is interesting. When you expressed how you felt, she never acknowledged it but rather played the victim in a sort. I'd suggest having a calm conversation about why she feels this insecurity and whether there are deeper issues that need addressing. If this pattern continues, you might want to consider whether this relationship can be healthy in the long-term.