There are 3 options with a nosey JW mom (I have one):
1. Lie
2. Tell the truth
3. Avoid (physically, verbally or a combination thereof)
All of the above carry consequences, so she will have to decide which consequence she can live with. If she isn't clear on a strategy yet, then I would strongly recommend cancelling or postponing lunch. Mothers have a way of getting to their daughters in a core shaking way. 😉