My sister has taken advantage of my dad with dementia and has taken over his finances. What can I do?

Qixtodd
You have posted this before.

Tell us what you have tried of previous suggestions. Did you call APS?

If you want help you need to communicate, have a two way conversation.

If you want to vent, that’s okay too.

Call APS (Adult Protective Services) and file a report of elder financial abuse. Be certain of your accusation, however, because it's likely to ruin your relationship with your sister permanently.

https://www.agingcare.com/questions/finances-and-sibling-rivalry-491822.htm