Jitsi works, and they have open relays to test with, but as the thing here is very much analog and I’d assume she’d just need to see your position, how hands move etc, the audio quality isn’t the most important thing here. Sure, it helps, but personally I’d just use zoom/teams/hangouts/something readily available and invest in a decent microphone (and audio in general) + camera.
That way you don’t need to provide helpdesk on how to use your thing and waste time from actual lessons nor need to debug server issues while you’ve been scheduled to train with your teacher.