Congratulations and commiserations on having a multi-talented daughter. The biggest problem of multi-talented kids is that they can only engage in some of the things which they enjoy and at which they are talented. High school or late middle school is usually when practice starts taking up too much time for a kid to have more than one or two time consuming activities like music or sports.
Unfortunately, your daughter is talented in two time consuming activities, and she is advanced enough that the time required to keep developing the talent makes it difficult to engage in any other time-consuming activity.
As for which is “better for colleges”. Once again, there is no “best” or even “better” EC for college acceptances, unless it is professional level sports.
However, even if there were “better ECs for college” that is irrelevant. ECs are not for college, nor are they for you. They are for your daughter. They are there to provide her with activities and stuff to enjoy which are not provided in the school classroom. Both music and physical activity will help your daughter with her academics, though in different ways.
My personal advice is that, if your kid cannot truly decide on her own, you two should decide based on how physically active she normally is. If your kid is normally and active kid, i.e., likes hiking, biking, rock climbing, etc, she should pick music. However, if her major physical activity is tennis, and if she does not play she would not otherwise engage in physical activity, she should choose tennis. My daughter chose dance over music, because of that reason. Of course, YMMV.
In any case, good luck. I would guess that, whatever the ultimate choice, there will be much fretting and agonizing, second guessing, and buyer’s remorse. However, I would also guess that, whatever the choice, she will, ultimately be very comfortable with the choice, and will excel in her chosen activity, be it Symphony Orchestra or tennis.