I don't know if you are talking about here on CM or in real life.
Here on CM, if she is corresponding, asking questions, answering your questions, is cheerful and nice to you, she is interested.
If you mean in real life, first, be sure she is not married or otherwise attached. Make sure there is parity and commonality between you (age, looks, background, lifestyle). If you have something in common along those lines, then I say just ask her out. That is the surest fastest way to find out.
If you ask her out for something specific and she says she is busy, she might really be busy.
If you ask her "would you like to go out with me sometime" and she says "yes" then immediately follow up with, "how about next (whenever)".
So there you have it...no time wasted, everyone knows where they stand!
All the best to you as you seek your vocation!