Clones are not like seedlings; they are ready too flower whenever you want them to. Its a matter of the size that will guide your decision when to start flower. Most stretch anywhere from 50 percent to 400 percent, so you don't want her too tall to start.

On another note, she looks like she has been growing in very low light. Clones should have that much plant material after a couple weeks at the most. Keep in mind that plants don't 'eat'' nutrients, they eat light, that is their food. She looks hungry for more light.