I agree partially.
I doubt that Kate knows that Ashe is a duplo. Nevertheless, I agree.
I disagree about Moira. She's a mayor and could get information about Ashe since her birth.
I'm not sure if it's a prank. I agree though that Bella can be a blackmailer.
If the blackmailer is a group they could have information about the kiss from a member of the group.
The blackmailer needs only Ashe's phone number, knowledge of her workplace, which is easy to get, and access to the party. Also, I highly doubt the liaison is into duplos because they don't know the most popular Ruby Phoenix whose photo Ashe sent as a proof of wearing the butt plug.
So, my idea is that the blackmailer doesn't really hate Ashe. If they would they gave her more competing or harmful tasks. They either want Ashe for themself (almost any of the listed characters), control her for some reason (e.g. Moira's control over Vanessa), get revenge (Jessica, Mrs. Leone, Brianna, etc.) or play her to get her out of her hole because they worry about her (Mom, Rachel, Fiona, etc.). The last assumption should not be declined because Ashe's life isn't going well for a whole year and the tasks ain't really harmful: explore sexuality, try new things, fix relations and fuck willing people.