2 WhatsApp accounts: 1 US/1Israeli; use US on ISR phone?

Hello,

We live in Israel, and my mother-in-law has her US number associated with WhatsApp but purchased a new iPhone 12 in Switzerland, where the salesperson created a new WhatsApp account, which she associated with her Israeli number, as that SIM card was in her old phone at the time. Both accounts work, but I would somehow like to A) get rid of her Israeli account and B) use the app on her new phone with her US number. Any ideas how? I'm stumped...