I think it would depend on which governing body of softball it's a qualifier for (ASA, NSA, USSSA, IFA, etc) and what kind of tournaments her other travel team plays. If it's an ASA qualifier and her other team plays ASA tournaments you have a problem because a player can't legally be on two different ASA rosters in the same season.
If it's an NSA qualifier (for example) and her other team doesn't play any NSA then you're probably ok.