ViRe VS VirtualMotionCapture

Not sure if it's still active, but you could check out ViRe: https://github.com/TrackLab/ViRe

ViRe: Another VR system. Only tracks head and hand positions, but that means you can use it with a basic VR system. Results are a bit janky, but useable. If you need more than the very limited head/hand tracking, you'll have to supplement it with another animation source.

The direct Link for the Release: https://github.com/TrackLab/ViRe/releases

ViRe on GitHub: https://github.com/TrackLab/ViRe

Or if you want the download directly, here is the GitHub: https://github.com/TrackLab/ViRe

Virtual Motion Capture is another free option which allows you to add your VRM model into the software and use your VR headset's trackers to move your model (Granted I prefered Liv's movements more). If you pay for their Japanese Paitron-like thing (300 yen, around $2.5 dollars) you'll gain access to the ability to send that tracking data over to vSeeface which would be preferable as neither of these two softwares provide bone physics or other customization that vseeface allows.

I suspect she is most likely uses something like Vseeface or VirtualMotionCapture (which integrates into VSeeface) and then loads that into her character app. Unfortunately the exact app might not be known. The character modeller for the new 3d model is jjinomu, who works in VRM format. Which means it's possible it could be anything from Unity to Luppet, VRoid Studio and some others. (Odds are though it's an off the shelf solution, as few vtubers are doing Unity/Unreal specific work.)