Considering how important 002 is to operate Star Entity, APE tried to clone her to create more candidates resulting in the Nines. However they were not good enough due to their blood being human.
Well, having taken a big chunk of hair from the Klaxosaurs' Princess, they probably had enough material to create more proper clones (or at least record said genetic code). Why did APE stop with just one clone?
With the amount of hair Dr. Franxx obtained, APE did attempt to create multiple clones. However, 002 was the only klaxosaur clone to survive.
Zero Two was created by Dr. FRANXX out of the Klaxosaur Princess's DNA. Many specimens like Zero Two herself were born but failed to survive; making her the only successful human-klaxo sapiens hybrid
(emphasis my own)
This is explained in Episode 21, in a conversation between Dr. FRANXX and 002.
Zero Two wakes up and says that 001 called her a fake. Dr. FRANXX says that 001 is the sole survivor of the klaxo sapiens, and she is her clone. She was created to operate Star Entity on behalf of the human race. He says that she was the only success
