On Android 7 the WebView implementation is provided by Chrome by default, to save bandwidth and disk space updating two copies of the rendering engine. If an app is directing you to update WebView, then the app is wrong: you should update Chrome instead.

So WebView should be disabled? Because my wife have the same phone and hers
isn't disabled.

Yes, it's expected to be disabled, because otherwise it would get updated by the Play Store unnecessarily. It gets enabled automatically if Chrome is disabled, to make sure you continue getting updates to the WebView implementation one way or the other, so if your wife's phone has Chrome disabled that would explain it (or if it's running an older OS version; this is new in Android 7.0).

Chrome is not disabled and she has the most up-to-date Android software.

Hm. That's unusual, then; it shouldn't be enabled in that case. If you're willing to collect a bugreport from the device we might be able to investigate why it's enabled on her device and see if there's a bug. https://tamingthedroid.com/take-bug-report has instructions on how to do this; you can send it to me privately (torne@chromium.org) and I'll take a look; you probably don't want to post it to the bug as bugreports sometimes contain small amounts of identifiable information.