iPhone 6 can't open What's app

My grandma's iPhone 6 with IOS 12.5.4 won't open What's app. The loading screen will show for a second or two and then a crash notification pops up.

We tried:

1. Restarting the phone
2. Checking if IOS and What's app are at their newest version
3. Reinstalling the app

I have no idea why it isn't opening. Thanks in advance.