Sakura would likely be initially terrified but quickly regain her composure. She is a trained ninja after all. She might start by assessing her situation, looking for any weaknesses in Team Hebi's defenses or any possible escape routes. Sakura would also try to talk her way out of the situation, using her intelligence to reason with Team Hebi. If that doesn't work, she would be ready to fight back using her taijutsu skills and any medical ninjutsu that could be used offensively, like her chakra - enhanced strength punches.
Sasuke would also be deeply affected. He might show his concern in a more reserved way compared to Naruto. He could be seen as being more determined to find a solution, using his skills and knowledge to try and save Sakura. He might even feel a sense of guilt if he thinks he could have prevented it in some way.
Sakura would be heartbroken. She'd likely spend hours upon hours by Naruto's side, trying to jog his memory with stories of their adventures together. She might even get a bit overbearing in her attempts. Sasuke, who has his own complex relationship with Naruto, would be conflicted. He'd see Naruto's forgetfulness as a sign of weakness at first but then realize the importance of their bond. Kakashi, being the experienced leader, would start by observing Naruto carefully to see exactly how much he has forgotten and then start a systematic process of helping him remember.
Sakura could also use her strength in combat. In the fanfiction, she may have developed new jutsu or fighting techniques that she uses to protect her teammates and help them achieve their goals. For example, she could use her precise chakra control to enhance her attacks and defenses, making her a valuable asset in battles.
Sakura would probably be angry at herself for being captured. She's a proud ninja. So she would start looking for weaknesses in Itachi's hold on her. Maybe she would try to engage him in conversation to find out his motives, all the while formulating a plan to break free. She could also try to send out some sort of signal to her comrades if possible.
She would be both curious and empathetic. Curious about how the baby ended up where she found it and empathetic towards the baby's situation. So she would start to form an emotional bond with the baby right away. She might talk to the baby softly, trying to soothe it, and then start making plans on how to best care for it in the long run.
Another reaction could be that Sakura tries to follow Sasuke. She believes that she can change his mind or that she can be of help to him. She might leave her own responsibilities behind for a while to chase after him, thinking that their bond is strong enough to overcome whatever is making Sasuke leave.
In some fanfictions, Sakura may be determined to find Sasuke and bring him back. She could set out on her own journey, facing various challenges along the way, and growing both as a person and as a ninja in the process of trying to reunite with him.
She might be heartbroken. Sakura could initially be in shock and then fall into a deep sadness. She may blame herself for Naruto's leaving, thinking that she could have done something differently.