What is the ruling on shaving a girl's hair at birth or thereafter with the intention of making it grow longer and thicker? Is it sunnah to shave her hair at birth by analogy with males?

It is not sunnah to shave a female's hair on the seventh day, as is the case for a male. Shaving a woman's hair is disliked (makrooh), but this dislike is removed if there is a proven benefit, such as stimulating hair growth and making it thicker.