I've updated the app to the new version on Android. After having spent an hour or more getting geolocation to work on my phone I tried signing into my wife's phone with her guest account in the new Android app.
She had forgotten her guest password and having spent another hour or more searching and trying solutions there's just no way.
This is so frustrating that I'm on the verge of tossing the hub into the garbage and switching to Home Assistant.
I'm not sure if it matters that it is a 'guest account', but have you tried the 'forgot password' link at my.hubitat.com?
Thanks for your help. As I was writing this question my wife was finally able to access the lost password reset where she was sent a code and then entered a new password. She doesn't remember where she got the link but she had saved an old email from 2 years ago where the link was included.
One would think that the forget password link would be in the login page... 
Thank you for your feedback. It seems like the link to recover the password on the mobile app is missing. You can expect the link to be added on the login page in the next update.
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