Morty has it, more or less. She used to be quite loud, but with not much body, now it's louder and gutsy... she has, if I may be so bold, bottom.

The diaphragm is the most misunderstood bit of singing... you really do need to learn how to use it. Having said that, learning to sing quietly but accurately is harder.

Opening the mouth well is a good start, but gaping like Brian Blessed on speed isn't. It is possible to make a loud noise through a relatively small hole, it all depends on what support you have underneath it. This is where the diaphragm comes in.

Keep persevering and one day it will come.

LTS