High levels of estrogen, as in first-generation COMBINED ORAL CONTRACEPTIVE PILL
, and progestin, as in some progestin-only contraceptives, have been shown to promote the lowering of brain serotonin levels by increasing the concentration of a brain enzyme that reduces serotonin.
Low levels of serotonin, a neurotransmitter
in the brain, have been linked to depression
However current evidence indicates low-dose combined oral contraceptives
are unlikely to increase the risk of depression, and unlikely to worsen the condition in women that are currently depressed.
Conventional pill contains 30-50 mcg oestrogen where as newer drug like gedarel contains only 15-20 mcg oestrogen so chance of depression is very low.
However if still your daughter feel depressed she should start an anti-depressant(Escitalopram, sertaline etc.). It may be quite severe later.
Just consult a psychiatrist