"Your cat is a queen, Sam."
Translation:قِطَّتَك مَلِكة يا سام.
In this case, should one use a ta because the animal is feminine? It accepted mine without a ta, so I'm curious to know whether it is normal to just add a ta (or ta marbuta) when referring to a feminine animal.
Any word ending in ة changes this letter to ت if a personal suffix is attached - including قطة. So your answer without ت should not have been accepted. What exactly did you write?
Note: ta (ت) and ta marbuta (ة) are not the same letters. Neither of them are added to any word - it is just that ة transforms to ت if a personal suffix is attached.
When we refer to a kitty without needing to specify its gender, it is feminine in Arabic, قطة ("qi66a"). A doggo is masculine, كلب ("kalb"). But you can remove the ة from "cat" to speak about a male cat, or add a ة to "dog" to speak about a female dog.