@Adi *******
yep, it's pretty straightforward,
all she'd be doing is changing the reason for her extension from "trailing spouse" to "being over 50 (retirement)".
She'd need to meet the proof of funds via banked money 800K baht in a thai bank account in her name only for 2 months before she applies
OR
by monthly income 65K baht a month transferred into her account from abroad or the affidavit of income from abroad (IF your embassy issues it)