Please help us to understand your question:
Microsoft have (idiotically) given the name 'Outlook' to two different things. Firstly there's a long-established piece of software (known as an email client) called Outlook, which is in the vast majority of offices in the country. It's used to send and receive email from any suitable email account. (i.e. the email address of the user could end in yahoo.co.uk, clara.co.uk, gmail.com, etc).
Then, completely separately, there's Microsoft's web-based email service which is (confusingly and annoyingly) also called 'Outlook', which has replaced Hotmail. (People using the service have email addresses ending in Outlook.com or Hotmail.com).
So which of those is your mother using?