Yes, a $10,000 conversion would be tax free if her total income is less than the standard deduction.
[Edited to add: I forgot about the Kiddie tax. See more below.]
A thought: Why does she have that much money in a traditional pre-tax IRA at age 20? You can only contribute compensation from working, and the contribution limit is $6000 per year, so she must have been contributing since age 17 at least. Why was she contributing to a tax-deductible IRA at all, why not contribute to a Roth IRA in the first place? I would not expect her income as a 17 year old to be so high that she would benefit much from a tax-deductible IRA contribution. Assuming she did, for whatever reason, she can do a tax-free conversion if her total income is less than the standard deduction.
Also note, if this is an inherited IRA, the rules may be very different.
