Hello Syed Hussain, please be fair in handling your employees. Are the salary hikes being given for the actual performance up to April or for the anticipated performance from April? I am sure I don't need to answer that - since you know it.
A Technical Head may be more concerned with the present performance/response of an employee. But, as HR, you need to be more concerned with both the present and future. Let the employee go in a happy frame of mind.
Also, the fact that you posted this thread makes me presume that you do want her to rejoin - please correct me if I'm wrong (whether she actually does or not is a different issue).
Another way of looking at the situation is from the employee's perspective: you aren't sure if she will join back - which means that she might also rejoin. Given the human mental mindset, if you were her, if and when you are in two minds whether to rejoin this company or join another company, would you rejoin if you are left out of the salary review process - even if you like the company in all other ways?
Another angle to this issue: I am sure you know that such actions in a company never remain a secret. The employees who are still present and would continue to work would definitely know about what transpired - and more importantly why. What's the unsaid message that you - as HR - wish to send to them? Hope you get the point I am making.
Hope you have the answer to your query by now - at least my take on it.
All the best.
Regards,
TS