<p>Some firms have rules that an employee couldn’t be rehired within a set period of time (like 18 months), especially if they have received severance. If an employee was fired for cause, then forget about it. </p>
<p>As far as writing to VP…the firing manager didn’t act on his own, he have had to consult the VP before he went ahead with firing the D. Even if the manager was wrong in firing the D, VP would be defensive of the manager’s action (assuming VP was a decent person). If he is just as bad as the manager or gets enraged after reading the D’s letter, he could decide to forward it to D’s recruiters or her new employer. OP’s D has nothing to gain and everything to lose by writing to the VP. That is another thing to remember, the D should not tell anyone at her old job where she is interviewing until she shows up at new job.</p>