That's because there isn't a freestyle at Prix St. Georges. The FEI levels only have the two (I1 and GP). But, because you can show in consecutive levels, you can do PSG and do a Fourth Level freestyle!
Assuming the rider is not of Young Rider age (16 - 21):
If she is competing PSG and Intermediare I at the same show, she may not compete in any 4th Level class, including the 4th Level Freestyle - at that show. She may, however, compete in an Intermediare I Freestyle.
If she is competing only PSG at the show, she may compete in the 4th Level Freestyle. She may also compete at 4th level in any class.
Thanks a million for breaking it down for me! I think her concern is that she may not be quite ready for an Int FS, but wants to try the test(s). In that case, she'll just have to do it in a different show than when she wants to do a FS. MUCH appreciated!!