Our singer as been asked by every soundman "is that how loud you sing?" She lacks volume. Some have suggested a microphone that would better pick-up her quiet singing voice.
We doubt that a different microphone would help. We suggest that your singer consider voice lessons to strengthen her voice.
Which Shure mics would you recommend?
Here's an analogy. If you have a little 4 cylinder, 100 horsepower car, it doesn't matter what kind of tires you put on it, it still won't be a race car.
In general, a condenser mic will likely work best for her, such as the KSM9 or Beta 87.