Thank you for entrusting me with your question. What step you take next is up to you, but there are generally two legal options: there is the criminal option and there is the civil option.
It appears that you have elected to exercise the criminal option by pursuing prosecution. The police are involved, the store is cooperating, etc., so what you can do is help in that investigation and pursuit to the extent possible.
The civil option is to sue the individual and perhaps the store for your damages. The individual is undoubtedly liable and your wife can sue him for her actual quantifiable damages, such as medical services, as well as her pain and suffering. Suing the store is not so easy; they would only be liable if the employee kicked your wife under their instruction or if they had reason to know that he would kick her as their employee--in most cases, an employer is not liable for the deliberate misconduct
of its employees. However, the store likely carries liability insurance
and most policies
have a "no fault" provision whereby the insurance
will pay a small amount even if there is no actual liability--usually it will only total perhaps $1,000 or $5,000, but it is better than nothing. Your wife, on her own behalf or through an attorney, may contact the store and ask for their insurance information so she can open a claim and see where it takes her.
I understand that you may have follow-up questions. Let me know if further clarification is needed. Thank you.