I've done a ton of things here but the latest that has actually given me some piece of mind is setting up a financial aggregator app with all her accounts + some basic notification rules for withdrawals >$X connected to my email. Obviously this requires a lot of trust from your parent, a lot of trust in Plaid (which I hate and worry about), and doesn't fully protect against the worst cases since it's reactive not preventive. But it's felt like a good backstop at the very least.
This entire process has been so frustrating and nerve-racking that I'd happily pay quite a bit for a "digital security for seniors" service if something like that existed.
Good luck!