I was fortunate to have voice therapy for 1.5 years before surgery. Anyone who had professional voice therapy learns to use the echo chambers in your head versus deep voiced males who use their diaphram.
The key is to keep your voice sounds above the neck. Then there are erercises to teach you to make your head the voice chamber. Some erercises are use to make you feel the vibrations in yoir head, words with m in it are used , e.g moons. Say moons and feel the vibrations at the nostril. Later when you can keep the voice above the throat and can feel the vibrations in your head you then work on pishing the sound to the front of the mouth. Females use their mouths more ... try making O shapes with your mouth and pushing your tongue to the top front teeth.
The key is not to stress your voice, nothing wrong with playing with a falcetto voice, experiment with mickey mouse voice but dont stress. In the end after much practice you will learn to use the head as the echo chamber and push the voice to the front of your mouth and open you mouth more in the O shape.
This should be natural, it can be tiring at first. Plus stand up when you are practising, if flem builds up try pineapple juice.
We all will have a voice comfort zone, mine varies from 190 to 223 hz as an average. The most difficult to keep a high voice is when you speak softly, its easier to speak in a high tone with a louder voice. Finally female voice pitch and tone varies alot as we speak,like singing. Experiment use your voice and have fun.