It sounds like she already has an identity with Intuit. She has two choices, try logging in directly to QBO with her existing credentials and reset the password.  Or use a different email and create a new identity.

Resolution for 'billing account issue: 'How can my client sign in to QBO after signing her up on my wholesale billing account?' available: Yes.

The billing account issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the billing account issue yourself by looking for a resolution described in the article. If it is a complex billing account issue or you are unable to solve the issue, you may contact us by clicking here or by using other billing account support options.

For more information about resolving issues related to billing account in Quickbooks/QBO or to get support for the issue 'How can my client sign in to QBO after signing her up on my wholesale billing account?', click the link below: