It's a little too convenient that right after Mithali found out about Avni being alive Dayavanti sends her a letter? Yes we know the goons were coming, and some woman was sending them. I bet Mithali has found out who this woman is, and it's probably someone who wants Avni and Co out of the house so they can sell the land to a developer or some such thing. This can't be Dayavanti.
Mithali knows all of Avni's history with Daya, that she died in a fire etc. So maybe when Avni told her not to reveal to Neil that she is alive, she still feared that if Neil knew Avni was alive, he would never leave her alone. Getting Neil to leave Kashid is proving tough, and Mithali already knows Neil is too curious about Jaan Di, who happens to be Avni. But only Mithali knows this fact.
I thought it was a bit suspicious that she spoke on the phone in a way that Avni could overhear where the goons were. She was hoping Avni would come there and she staged that whole Daya's burnt hand paying money stuff. She also faked her attack. Now she has convinced Avni that Daya or someone who knows of her is after them. So for the kid's safety they should leave. She is ensuring that even after Neil leaves Kashid he wont have any contact with the Sukoon house crowd. After all, Neil knows Suneheri and Tara Sitara and he has grown close to the kids too.
This is ALL a plot. That's what I believe. And I was right! Neil and Avni ARE meeting in Mahabaleshwar coz that is where KK is going next for his shoot.
Let me know your thoughts!
Mandy