Why would quickbooks drop one of my users, when she was using it yesterday?

No she can't, and I have tried setting her up again, but it says that the user ID is already used.  Then I have tried adding her again using another email address but it goes through the process of signing in to Quickbook Online and then it says that QuickBooks Online is not open and to select another option.  We have also tried to recover, however this sends you in the same circular procedure.  Getting very annoyed.