A couple of things to consider, a J frame with full power loads is no fun to shoot, 600 rounds is going to beat her to death.  If she tries to shoot a 600 round course with full power loads in a J frame, I really doubt if she would be able to complete the course, you should look into getting a hold of a full size 38 revolver for the course.
I don't know the course, what is the maximum range they shoot?  The sights are designed for standard weight bullets, lightweight bullets shoot low, 125 gr bullets in a 38 can shoot a couple of feet low at 25 yards, that is enough to cause serious problems when shooting a course, at 25 yards the bullet impact of a revolver aimed at the bullseye could completely miss the target.  Any loads used should be close to 150 grains so that won't be a factor. I would recommend a light load with a plated bullet of about 150 grains, an old standard load was 148 gr wadcutter or 158 gr round nose, or a semi wadcutter could be used, with 3.1 gr of WW231 or 2.5 gr of Bullseye.  
Cast lead bullets could be used, they would be very dirty, or a better choice would be plated bullets, much cleaner than cast bullets, but the gun is going to get really dirty no matter what kind of bullet you use,  but it will be much dirtier with cast bullets.  Revolvers are inherently dirtier than autos, no matter what loads are used, that gun will be filthy, an old T shirt with some powder solvent on it to wipe the gun down from time to time would help.