Keep the details of the deleted bill intact.
I would suggest to keep the details of the deleted bill intact even if it is deleted. Allow viewing of the deleted bill in detail from dashboard instead of just showing a message in the event list that the bill was deleted. This will permit viewing of any bill that has been deleted by mistake and any unauthorised delete can be detected.
If you look at a deleted bill in the Android and iPhone app from the recent activity feed, you can see the details of the bill and undelete it if you want.
Deleting ability should be limited to those in that subgroup. Just went on a large group trip...I thought I was “deleting from my view” as I wasn’t involved in some charges, only to realize I was completely deleting the item as an expense. Not a good or intuitive UE.