My 9yr old ds had to have an MRI on his head (brain) a few weeks ago.
I was allowed to sit in the room with him and could see his face using a mirror and touch his legs which were sticking out of the machine.
The worst bit was the noise and having to keep still for so long.
At least he had a chance to hear the noise, if somewhat muted, through the very thick door before we went in. We were both given head phones - mine just to keep the noise out, his he could listen to music through. He chose what music to listen to and we worked out that he woud have to keep still for about 4 songs, so it gave him a benchmark.
Your dd will have to remove anything metal that is loose - jewellery, mobile phones, coins and leave them outside the room. As the strong magnets could make these items dislodge and fly around the machine! I was allowed to keep my underwired bra on though
the radiographers looked after all our bags and valuables.
It is painless, very noisy and a bit uncomfortable having to lay still but being terrified about it, ds actually thought it was quite cool - but he is only 9

Hope it goes ok and your dd gets some answers.