There is no hard and fast answer. Your sister clearly isn’t part of the group they are really targeting but it all depends the what the IO in front of her thinks.
they will likely extend consideration to ASEAN passport holders. This is for the nationals who are abusing visa waivers to maintain residency. All of them can simply apply for DTV, O, LTR or privilege.
Are those flawless? No. They can definitely use some streamlining but they add better control than a tired IO at 2 AM
For purposes of having 800k in a Thai bank that is sufficient. How it got into the account doesn’t matter for the 800k method. It only matters for the 65k/month method