Her capacity for Life Energy had increased over time as it steadily grew higher and it was almost like she had built herself a more stable source of Life Energy during that time that was more under her control.
It did seem like her steady increase of Life Energy and letting it slowly become her own had made it so that her Life Energy was not unstable or had other issues due to being hastily increased in a way that could hurt her body.
If the body was the vessel to contain that power then it needed to be strong enough on the inside and outside to contain such power.
If the power was unstable then a strong body was needed even more to be able to contain it and get it under control otherwise it could end up damaging the vessel.
Adding Life Energy could increase the capacity the body could hold like she was doing but even a strong body had its limits on how much it could be pushed beyond its limits.