Ulysees you're so right about beginners paintings having more life in them. You tend to find that people who study art at a level or degree level are so tightly conditioned by the tutors (who want to "discover" the next Damien Hirst) that their work loses the freshness of when we started out.
I do portraits , but artschool sucked the love for it out of me. I'm quite envious that you've found a love for painting later on, I wish I could start again!
What kind of things are you painting at the moment, and which medium are you preferring to work in? I never got on with watercolours as they weren't gutsy enough for how I work, but used acrylics for years before moving onto oils, beautiful thick rich colours!
Don't worry about using particular brushes, I never tended to have enough money to afford many. For my purposes I had a few DIY style paintbrushes for blocking in backgrounds and large areas of colour, then a good quality medium sized brush for sketching in the image, working downwards in size to a small detail brush. But a lot of the time I would use my fingers as they're more sensitive and controlled. Always good to have a million rags about and a pallette knife or two if you're using oils, to scrape off anything you don't like.
Tell the silly woman who keeps screwing up her work to stop, as while she might feel frustrated now, it'll be good to have a record of her progression! And anyway it's a waste of materials. She could easily paint over the image later on and start again, or use the back. (Can you tell I was a skint art student for years?)
Anyway sorry for rambling on!