Unauthorised absence - employee on probation period was till date not issued any extension letter

One of my employee was on probation period which ended up on 31st march 2019. Though being at a senior position she was till date not issued any extension letter and was coming. However she is absent from 5th April. what course of action can be taken against her?

Your company is at fault.
If probation was over on 31 Mar 19, she should have been given or informed that she is not being given confirmation.
She has taken advantage o of that and stopped coming.Call the employee over and discuss the matter,if you want to retain take proper action on paper and if you do not want to continue,inform her accordingly and relieve her.
By the way does your company have HR department?