We also never get an explanation as to why she has just two external Borg implants left--the one over her left eye and left hand. Maybe they're benign enough and actually provide a benefit, that it was decided to leave them in. Certainly the internal nano-probes are still there, as well as the tubule stingers.
That implant on her face is actually just the tip of the iceberg. In "Timeless" we were shown that inside her head it's a massive implant.
Likely the one on her hand comprises most of her hand inside her skin.