There would be a number of factors to consider .....
Statistical likelihood of finding a pathology .. for example, in a healthy adolocent one would not expect to find very much pathology .. i.e. cancerous tumors .. however it is not impossible either. But generally no. Also, one would expect a young woman's body to be going through tremendous hormonal changes and that there may be things like galactorrohea (producing small amts of milk without pregnancy) or small amounts of clear discharge, which is normal. Some minor pain or tenderness of her breasts or nipples .. etc .. but nothing too serious. Anyway, a young woman like that would probably only need a cursory check to see that things are generally "ok". There are some psychosocial issues that need to be addressed. A young girl who is beginning to develop is going through some tremendous changes, and she probably has little idea of what normal is and of course there is the angst of hoping that her breasts develop to the fullness that is the symbol of her femininity that she watches develop with some understandable angst as we as a society put so much emphasis on a woman's breasts. Some reasurrance from the Doctor or probably a female Nurse is probably appropriate and really .. should be done.
A lot of consideration for how thorough the exam should be would be the all important history. Did she present complaining of breast issues? What were those issues and is there a reasonable explaination for them?? Has she had prior breast augmentation surgeries?? This may seem silly but it is reasonable to ask ... is she pregnant??
Clinical breast exam should follow pretty standard methods ... Observation with various positionings to accentuate any dimpling, retraction, or other inconsistancy deemed abnormal. Then palpation both standing/sitting and supine. Not forgetting the tail of the breast that extends toward the armpit. As far as how thorough the exam has to be has much to do with the presenting symptoms and history. Remember, one is feeling for something that could be as fine as coarse cornmeal.
In cases where the primary "complaint" is nipple discharge .. especially if it is just one sided, for which there is no reasonable explaination, The Doctor or Nusre will be very thorough. One new diagnostic option is called a ductal lavage (google that up) .. some offices do not have the whereforall to do that procedure or even if they did, would probably first try the traditional "milking" of the nipple(s) to acertain if and how much discharge there is and were it is coming from. In this case, a woman can expect to have her nipple(s) and maybe her breast proper "vigorously" massaged and squeezed. It will probably hurt but will fall short of leaving bruises. I'm not sure if it will be of comfort to the woman but if indications for this thoroughness are there ... whatever tenderness is a small price to pay for making sure that nothing is missed.
Anyway, all womens breasts deserve all the attention that is indicated. And the thoroughness will take in all the factors that I had mentioned and more.
I personally feel that a medical person should be designated as one who does thorough breast exams because the feel and texture of a woman's breasts are as infinite as there are women. And it is from the handling of thousands of women's breasts that one knows whether what he/she is feeling is normal variance or pathology.
Please ask if you want to know more about ductal lavage
Warmly
Will