For speech to be libel, it has to be false.

This doesn't sound a case of libel, you can harass someone someone without using false statements so I'm not sure it would be relevant.

This seems confusing and I doubt she'd be willing to publish a DNA or testosterone test as she didn't go to the CAS after her '23 ban.

The organization that gave her the ban is no longer recognized by the IOC or CAS, so again not really relevant. Not really relevant either way, if you get false claims made against you by a corrupt organization you're not obligated to go after them privately or legally. Like I'm sorry, I'm not taking any claims by the IBA seriously.