Ask HN: Calendar Sync/Scraping Tools?

Hi HN. Long story short: my girlfriend is a massage therapist being squeezed for big commissions by treatwell.com, a booking calendar and SEO service. After she signed up with it, treatwell curtailed the ability to export data from treatwell's calendar to her google calendar, probably as a deliberate lock-in tactic. Although treatwell reads her google calendar to avoid clashes, it writes only to its own when someone books through treatwell. With her clientele steadily increasing through independent referrals, she's investigating alternatives including self-hosting, but assuming it's not worth ditching treatwell entirely, what tools would you recommend for scraping her treatwell calendar to keep her google calendar in sync with it?