Can I switch from a 60-day visa exemption to a retirement visa in Thailand with sufficient funds?

You can meet the proof of funds (800K in a thai bank account in your name only), plus you need to have enough time left on your 60 day visa exempt entry (usually a minimum of 15 days or more) and at MOST offices apply first for the in country 90 day Non-O visa based on retirement for 2000baht

Go to your immigration office and get the hand out listing the requirements to do the in country 90 day Non-O visa based on retirement.

Keep in mind not all offices can/will issue in country Non-Immigrant visas, so if they don't you may have to go to a thai consulate in a nearby country and get one then come in and apply for the year extension when you have 30 days or less left on it

Sadly that you have a thai granddaughter doesn't cut any ice with immigrations as far as any visa you could qualify for 😕