Roth vs Traditional has to due with the income tax rate you expect to pay now vs that in the future.

It is impossible for you to predict the advantages of Roth vs Traditional 40 yrs from now. There are just too many ways for the government to tax you. For example the government could eliminate the income tax and tax go with a sales tax. On the otherhand the govenrment could raise income taxes to pay for the huge deficits. That would make the Roth worthless.

BTW, a twenty year old should pay the most attention to her future earned income. I hate to say this but a sharp suit, or golf lessons/practice might have better returns than an IRA.

I personally would suggest a Roth.