Cervis would indeed notice the chakra flow and the activation of the jutsu that targetted the water near and within the plants; by flowing natural energy and mokuton chakra into the wood, Cervis would be capable of prolonging any problems caused by the rogue water manipulation.
What was the purpose of this delaying action? Well, it was two-folded: it would allow Cervis to coordinate an attack on the man, increase the pressure within the plants themselves, and layer his wood release with more, how one might would say, wood, though of the dead variety that had little to no water in it to start. This would make Rita's restraints somewhat more bulky for the time being, but it would prevent the bursting of the wood, at least for now.
"Water release, and explosive release hm!"
Pyro did not see nor really sense much of any change, save for the transformation of the water drops to ice upon the man's armor. This ruled out a physical attack on the individual, and so Pyro called forth several balls of scorch release chakra. Pyro would then direct a volley (6) towards Jay. Each ball of scorch release chakra had the capability of mummifying the average man, with temperatures so great that the drops of water around it merely evaporated before coming into direct contact with the balls.
Shakuton: Kajōsatsu – Scorch Release: Extremely Steaming Murder
Expecting his quarry to dodge the first volley, Pyro readied another volley, already combining it into a much larger scorch release ball than before.
Light. Light had never been so welcoming, so warming, than when Pyro readied his scorch release balls. Rita, unlike Pyro, could sense the chakras of her restraints, and then, having used her small down time to regain her wits and assess the situation, she ascertained that the man indeed had intentions on freeing her, or at the least using the water in the wood for a sneak attack. What with Cervis attempting to resist only increasing the danger and imminent threat to her, Rita funnelled her built up chakra into her mind and shadow; the moment that Pyro's lights directed Cervis' shadow within reach, Rita's own shadow would snap at the connection like a predator would its attempting to flee prey.
The intent was to subject Cervis to a genjutsu that would bind him in a tree made entirely of shadow tendrils; much like its parent technique, it would bind the user in a genjutsu with aforementioned visuals, but it would also bind the target physically via shadow imitation. If Jay were much of a sensor he would likely notice Cervis' chakra signature alteration and that the conjoined shadows seemed to defy the light of the fireballs, albeit, his focus may have been more on dodging those than anything else.
Dragon Illusion: Shadow Tree Binding Death; Ryūgen:Kage Jubaku Satsu
More importantly, this restraint would be intended on leaving an opening, for as long as Rita kept up the shadow connection the alpha deer would be trapped, both body and mind, and be unable to sustain jutsu nor dodge the man's next attack, presuming it did not involve breaking the connection between the shadows.
Cervis would not be caught entirely off guard by Rita's attack, but between trying to keep the wood from bursting (so that Pyro would not assume he had renegaded on the deal and try to kill him) and staying alert for the man's retaliation, his options were tied; he would be bound by a tree of shadowy tendrils, but also release his hold on the aforementioned jutsu, causing the wooden restraints to, at this point, burst with greater force than before. The wood shrapnel would now likely have the force to get through some of Rita's scale armor, but not quite enough to go completely through her; large and painful splinters would be her reward for her disregard for Cervis' cause.