It's possible that you may be able to find the parties' submissions on the court's web site (where I found the decision of July 29, 2019, in French), but I haven't tried to find any of those filings. Based on the court's brief summary of the arguments on appeal, it appears that Semenya limited her grounds to two allegations of substantive (as opposed to procedural) public policy -- first, that the CAS decision violates her rights against impermissible discrimination by upholding this particular IAAF regulation that differentiates on the basis of sex and innate biological differences; second, that the CAS decision violates her rights of personality ("personnalité") and human dignity guaranteed by, among other things, various treaties. The court deals with each of those arguments very summarily. (The court's summary treatment of the decision in Matuzalem is mildly irksome, but I don't recall the details of that case.)
I want to clarify an important point. The court did not hold that the appeal "will ultimately fail." Rather, it held that Semenya (and, to the extent it has standing, ASA) failed to show that the appeal is very likely well-founded ("La condition du caractère très vraisemblablement fondé du recours n'étant pas réalisée"). This appears to be very similar to the standard in U.S. courts generally requiring a showing of "high likelihood of success on the merits" to justify preliminary injunctive relief, including certain stays of lower court judgments. It is, however, a bad sign for Semenya that the court expressly held that, in light of her failure to show a high likelihood of success on the merits, the court did not need to reach questions about the extent to which Semenya is irreparably prejudiced by the CAS decision.