The main issue related to her ability was that there was only so much Life Energy she would have to use, so she had to be smart with how she used it in different situations.
If she wanted to keep one form, then it would usually be more efficient to transform into it and to hold it until her Life Energy started getting low.
That method would be quite efficient since the cost of it would be far less and would allow her to maintain the form over a long time within the limits of her Life Energy capacity.
The main problem was that once she had used up all of her Life Energy, she would not be able to transform back so easily, and she would be drained of her Life Energy, so it would take more time to regain everything.
There were situations where she would have to make use of her transformations for a longer time, so that approach would be needed, but not every situation would require the same approach.
