Some companies, including in education from my experience, only have one reference form and it is for employers.
I was filling one in just yesterday for someone I know professionally, have worked with maybe four times over the last year (less frequently than usual due to Covid) but have never employed, or even worked in the same organisation with.
I put 'N/A - I have never employed X' for a number of the questions, such as how many days absence have they had in the last two years, or what was their job description when employed by me, and left blank some of the tickboxes where I had no knowledge.
In the section on suitability for the role, I wrote how I knew them and for how long, and that I could comment on the following relevant aspects.
I emailed the reference with the covering note that I had not ever been X's employer, so could not answer some of the questions but would be happy to clarify anything if they needed more information.
In your case, I would check with the girl what she said your relationship with her was. I actually always ask to see the application of anyone I am writing a reference for. If she has lied, then refuse to be her referee.
If she has been honest, I would fill it in as best you can, like I described above.
It is fairly standard, although a bit annoying and awkward.