I was very fortunate that although I struggle with rhythm, and sight reading, that my parents allowed me to try a number of instruments.
I could only get to grade 4, as beyond that you need theory exams, and had to have rhythm. I have grade 4 in percussion, violin, piano, saxophone and flute.
On the other hand, my sister, who doesn't suffer from my lack of rhythm, has grade 8 in both piano, and trombone, as she focused on these two and didn't want to learn other instruments.
IMHO I would say your dd is 7 years old, would love to learn another instrument, let her do it. Who knows if she's going to be in the orchestra when older, she may decide at 14, that she's having fun, and doesn't want to have formal lessons. So be it, give her the opportunity now, whilst she wants it.