It’s a sign that she’s physically comfortable with you, but not necessarily a strong indicator of romantic interest.

Like most things, it depends a lot on context. If she’s leaning on you for support while tying her shoe, that’s not very significant at all. If you’re sitting side by side and she leans her head on your shoulder that probably indicates some affection, though it need not be romantic.

It’s generally impossible to be sure someone likes you from hints and signals alone. Some people are totally blind to such signals, while others are apt to over-interpret every little gesture as a sign of interest.

It doesn’t really matter though. Whether she was signalling that she likes you or not, if you ever want to go out with her you’re still going to have to put your cards on the table and ask her out. Until she actually asks you out herself, that’s the only way it’s going to happen.