It depends on the age of the gymnast. If she is not old enough to be petitioned into Level 6, she would have to score out of both levels. There is no direct mobility FROM Xcel to DP.
From page 77 of the R&P above, "Any gymnast who has had previous competitive experience other than USA Gymnastics but including USA Gymnastics Xcel athletes, and who is a minimum of 12 years of age is eligible to petition by submitting a formal written request to the SAC for entry into Level 7 and below. The petition must be accompanied by a video that demonstrates her skill level."