I assume this will do it. Not sure why its a nightmare.
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onlinehelp.microsoft.com ··· 382.aspxFor home premium there are no additional account users other than the one who owns the account. If you activated the subscription with her credentials and not yours, you've made an error. Perhaps that is your nightmare?
You'll probably have to call Microsoft to get it sorted out. Or, if you want to do it yourself, you'd cancel your current O365 subscription (and get a refund) and sign up for a new O365 subscription (and use the correct live ID when activating it.)