Why are her nipples leaking?

Lactation (milky nipples) occurs with the production of the hormone Prolactin. Prolactin can be produced for a number of reason, most common with pregnancy. If she does not look pregnant and she is lactating, she probably isn't pregnant- pregnant women don't usually lactate until they are showing their baby belly.

Excessive stimulation of the breasts and nipples can cause lactation. Touching, biting, sucking and pinching the breasts and nipples can trick the body into thinking that there is a baby that needs milk, therefor the body will lactate.

Another explination would be birth control pills. Certain birth control pills can cause lactation, and abruptly stopping birth control pills can cause lactation.

Sometimes when women have breast cancer their nipples leak something that could be confused with milk but actually isn't. This probably Isn't the case but its better to be safe then sorry! See a doctor!

she needs to see a doctor- the test could be wrong. milk ONLY comes out of breasts when the body is either about to go into labour OR ... there is cases where if the body senses theres a need (ie. maternal instincts take over about another child OR her body is convinced she is pregnant)