iPhone network compatibility

Thanks! My daughter on my Verizon Plan moved to rural Colorado. Her husband's ATT iPhone works while hers works just barely sometimes! She asked me to get her a new iPhone 11. My experience on older iPhones is YES! So if a new iPhone 11 fixes the issue, all is good. If not she can get a new sim and move to her husband's ATT plan and save me cost of her new phone in short order.