iPhone 8+ or Upgrade a 78 Year Old

Coming to the forum with a question many of you with older parents probably consider.

My 78-year-old mother has an iPhone 8+, but the battery is going out. She loves it, and is concerned with her limited mobility (she had a stroke) that she will have trouble operating, say an iPhone 13. So I'm considering just having the battery replaced.

My other option is to purchase a premium refurb iPhone 13 for $349.

She's on the US Mobile lite plan and uses very little data. What do you think?