First off, are her wings clipped?
Secondly, don't sweat it--It's only the first month. I adopted my cockatiel, Colby, in August. He was very shy his first month, but after a while he began to relax and show his true colors. Something useful may be target training. Use a chopstick or other small pointer that you aren't using for any other purpose, and place it through the cage bars or near where your bird is perched. Remember to introduce it slowly, and remain calm even if she is frightened. Hold the millet or other treat near the end of the stick. Once she is comfortable touching the stick in exchange for a reward, you can teach her new tricks and make your bond with her stronger.
Some cockatiels take longer than others to trust people. Judging by your situation, I'd expect this to take two months at the very least to get her moderately tame.
By moderately tame, I mean that she steps onto hands willingly and doesn't hiss quite as frequently.
I read to my bird and allowed him the choice to come out of his cage. A t-stand may be helpful for such purposes, if you need to transport your bird around your house or for training. Is your bird comfortable being on a parrot play gym? Is her cage large enough? My cockatiel was very territorial of his cage until I got him a larger one. Does she enjoy preening toys? I've read that most cockatiels do.
There are several YouTubers that have some good information, but remember to take some of their advice with a grain of salt. I've found that ElleAndTheBirds has excellent information on bonding, taming, and dietary conversion of birds. Other members of the Avenue have plenty of knowledge to share as well.
I have used a towel to catch my birds when they weren't tame in the past, but with a bigger bird it can be difficult to do so. If you feel that their could be underlying issues or behavioral problems, you should consult an avian veterinarian or your local bird rescue.
The Parrot Problem Solver by Barbara Heidenreich discusses many of the problems that you have mentioned. But please understand that it can take years for a bird to trust you. Don't give up on her or yourself! You've made a lot of progress already. Please keep the Avenue updated on your progress with her in the future