[+2]: You gain 1 life for each creature you control.
[−3]: Creatures you control get +2/+2 until end of turn.
[−9]: Put X +1/+1 counters on target creature, where X is your life total.
Ajani’s second ability affects only creatures you control at the time it resolves. Creatures you begin to control later in the turn won’t get +2/+2.
The value of X is determined only as Ajani’s third ability resolves. If your life total changes later, the creature won’t gain or lose +1/+1 counters.