How do I tell Mum I want an interpreter at her appointment?

Mum handed me her hospital letter and said, "You know both languages. Why would we need a stranger?"

I can discuss shopping, school and family arguments in either language. At her last appointment I stumbled over a phrase about the proposed procedure, then used a word that I later discovered was not quite the same thing. Mum thinks I am being dramatic because the appointment ended without an obvious problem.

She wants me beside her at the next consultation. I want that too. I do not want to be responsible for making medical information sound more definite than I understand.

The hospital has told us to contact it about interpreting needs before the appointment. Mum is worried that an interpreter will replace me and make her feel alone.

How can I explain that I am asking for help with the language, not trying to withdraw my support? I need to speak to her before contacting the hospital, rather than present a booking as something I have already decided for her.