How does a Guardian login to the SyncUP app?

I added my sister as a guardian on my kid's SyncUP 2 watches. She received the invites and downloaded the app when instructed. Now the app wants her to login. This is what I need to know... Does she use my login info? Does she create her own login info and profile to get into the app? Or does she use her husband's login info for their T-Mobile account? 

I can't find any info on what to do after downloading the app. Please help!! 😭