String teacher here.
You can so easily find music that is the correct key and difficulty level yourself. If you're unsure im sure the teacher will send you some suggested music to buy.
You say you want it arranged, so that implies you want her to write it out herself. This takes time, are you going to pay her for her time? If so it would be much cheaper to find out what music to buy and get it on world of books/eBay etc. If it has to be arranged there won't be a backing track will there? How will there be a backing track for a piece of music that is bespoke arranged by the teacher? Are you expecting her to record one? Again, she would need to be paid for the time it takes to do this, so id again refer you back to simply finding the correct music second hand somewhere.
All my pupils buy their own music. I do not buy music for all 50+ of my students. That would be very expensive, and as I only make about 15k a year this would not be tenable.
What you're asking is not for the teacher to "be accomodating", you're asking for a huge amount of work to be done by her.
I celebrate Christmas, and I have written out the odd Jingle Bells here and there but they all like to go and find their own music that suits their taste and ability. They know what to look for.
Even a new book is only like 6 quid or something, and you will get lots of use out of it. If its Christmas stuff you'll go back to it year after year, so you'll get your money's worth.
When taking music lessons myself I have always always provided my own music
As has every other musician I know, which is lots of people.
Hope this helps.