Most of the adjectives in Italian have 4 forms, as in: stanco (m. sing.), stanchi (m. plural), stanca (f. sing.), stanche (f. plural)] leggero (m. sing.), leggeri (m. plural), leggera (f. sing.), leggere (f. plural) bello (m. sing.), belli (m. plural), bella (f. sing.), belli (f. plural)] There are (of course!) also variations on this scheme, as in: pesante (m. sing.), pesanti (m. plural), pesante (f. sing.), pesanti (f. plural) Also the colour names sometimes are grammatically adjectives, and therefore change their forms. rosso (m. sing.), rossi (m. plural), rossa (f. sing.), rosse (f. plural) il prato verde (m. sing.), i sassi verdi (m. plural), la foglia verde (f. sing.), le olive verdi (f. plural)

if you are female, you should say "sono stanca" the final -a means you are a female

If you are female you should "sono stanca" because you're female. "Sono stanco" must be told when you're male.

Yes you should say: " sono stanca".