If you can't cobble together a consistently-profitable trading plan in demo, you sure as hell aren't going to be able to do it live. And without a consistently-profitable trading plan, you may as well rake all your money into a pile and set it on fire. At least you'll get some pleasure out of it.
The chief problem with demo, aside from the sometimes optimistic fills, is that the beginner doesn't take it seriously. He'll wait a second or two to determine whether or not the trade he thought about taking was working out, then think to himself that he would have taken that, which is a step toward telling himself that he did take it. That can lead to disastrous results when transitioning to live trading. Or he will literally trade the past, like reading an old chart from right to left instead of left to right, and persuade (delude) himself into thinking that he's got this hot system which is in reality a bunch of crap.
At the very least, if he does it right (or, in your case, she), he can/will learn discipline, which is absolutely essential. If he can't/doesn't, he may as well move on, and the sooner, the better.