using the genesis regeneration doesn't really use the chakra in the caster's body.. it uses the chakra from that point on her forehead where she had been gathering it for a lot of time. she seems to have some technique with which she can store some of her chakra every day to be used for the regeneration technique when in dire need. the weakness is that it regenerates you by basically aging you faster, and thus reducing life span.
so she used some heavy duty healing a couple times, and summoned the slug queen. that doesnt use incredible amounts of chakra...