Depakot as prophylactic?

My 15 yr old niece has a family history of bipolar disorder (grandmother, mother, aunt, and brother). Her doctor is prescribing Depakote as a prophylactic measure against future bipolar disorder even though she is stopping short of diagnosing my niece as bipolar right now.
My niece has had some depressive episodes over the last couple of years but has never had a manic or even hypomanic episode.
Will starting Depakote NOW somehow lessen the severity or prevent or delay the onset of "full-blown" bipolar disease?
I understand that my niece's family history would indicate a high chance of her developing bipolar - but is her doctor jumping the gun here?

Furthermore, can you direct me to any studies regarding the long term effects of Depakote?

[Roger Gould, M.D.]

I do not know of any credible research that justifies using Depakote as a preventative medication.  It has side effects, and numbing effects, and is usually consider safe for long term use, but shouldn't be used at all unless strongly indicated.

[annelrm]

I took depakot for a  few weeks and it made me so sick, I heard a lot of bad things about depakot. It is supposed to be for people with epilepsy.  If I were you I would get her off of it

[I'mallheart]

get her off it ...its bad especially on the liver...