1. well i've never done a truth spell before, but it could work. depending on why the person is keeping a secret could determine if it would bring harm or not. meaning lying to not hurt her friend. but a truth spell that won't case the person to become physically injured, yes, those exist.
2. you could try a simple candle spell. use a white or blue candle, charge it with energy then light it, and think about her telling you the truth. [if you want to say a chant you can] let the candle burn out, don't blow it out [as that will undo the spell] if you must put it out, snuff the flame. for this type of spell though, i think i would wait until the new moon or waxing moon phase to cast.