Oh, cello is so beautiful, don't say "she'll be stuck with cello". Funny that viola is so popular, folks must have realized that there was a shortage for so long that if you played viola you had a better chance of being a first viola or getting into the higher group.
Our music teachers check your emboucheur and musicality and experience and make recommendations for you, but of course the final choice is the family's. My older son was recommended for...I don't remember, because he wanted to lay percussion. The teachers said they strongly prefer piano experience for percussion (different clefs and for mallet instruments) but he wanted percussion, so he did. My younger son was recommended for clarinet or oboe and I'm so glad he chose clari, I don't care for oboe. He's doing vey well, too. He took summer trumpet lessons a couple years ago because "Mom, the cool kids play trumpet", but it didn't suit his emboucheur or his braces. And cool kids are throughout the band in high school, so there.
At 8 or any age, piano gives experience in playing and hearing more than one thing at a time, and can take you everywhere since you also learn clefs, rhythms, etc.
Have you considered also guitar?
