11 yr old has smelly scalp

My 11 year old in the last year or 2 has developed smelly scalp.  No one else in the family has it and the children and I often share hair brushes so it does not seem contagious.  I had grandma double check but no one else's head stinks and my younger kids actually smell really good.  
During the summer when she swims in a clorinated pool and washes her hair every day the smell subsides.  Which makes me think it is fungal or oil.   During the winter her hair looks oily and stinks immediately after she washes her hair.  I smell her head when it is still wet just out of the shower and it still stinks.  She hates washing her hair so right now it only gets washed 1 or 2 times a week and I keep on warning her it smells from a distance.  I don't think washing every day would help without swimming which is not available.
Is it hormones? She is starting to develop breasts and is moody.
Is it fungal / bacterial?  She has had antibiotics years ago so does she need Probiotics or acidophilus?  (but it is not contageous - I have used her hair brush and only wash my hair 1x week and no stink)
Is it oil?  I had oily hair as a child without stink?
Please help!

[Bhupinder Kaur, MD]

Hello,
Two possibilities are there for your symptoms. First of all,stress or hormonal changes may lead to excess oil produced by the oil glands in your scalp. This causes the harmless bacteria that live in the scalp to proliferate and feed off the oil, which produces the odor.

Second possibility is of a fungal infection causing tinea capitis. It is contagious and can spread direct contact with someone who has the condition, or if you touch contaminated items such as combs, hats, clothing, or similar surfaces. Diagnosis is by clinical examination of the scalp as well as a skin lesion biopsy with microscopic examination.

It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.

[busymom3CA]

Well it turned out that my daughter was washing her hair without scratching all the old stinky dead skin / dandruff off her scalp.  I started washing her hair for her and scratching or combing all the gunk out.  Now she does it herself.  Her scalp stink is much improved although she still hates washing her hair.