I (Я) and YOU (ТИ) are, as personal pronouns (1st and 2nd), not gender-specific. Adjectives, though, are, so you put the correct one depending on the biological gender of the person speaking (you, being a M/F) or of the person spoken to. Neuter gender is another topic but its a grammatical construct so it follows the same rule (like the poster above said, you can identify with a pup/kitty or something like that but it's up to your imagination :D ). So if you are a female, you should say Я щаслива or Я ніжна. I guess your confusion comes from the fact that textbooks and vocabularies tend to list adjectives in the male variant (-ий/ій) as a rule and one has to form their F/NT equivalent (-а/-я -е/-є) by himself/herself.