Yes, COWHERB is a Scrabble word!

Letter values in Scrabble US: C 3, O 1, W 4, H 4, E 1, R 1, B 3.

Is it a valid word?

COWHERB is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

European annual with pale rose-colored flowers; cultivated flower or self-sown grainfield weed; introduced in North America; sometimes classified as a soapwort

Also: cow cockle, vaccaria hispanica, vaccaria pyramidata, saponaria vaccaria.