Experience / relieving letter

If the employee was terminated for unacceptable/improper behavior, the company is not bound to issue a positive experience certificate.
At most, the employer may issue a service certificate (as per Shops & Establishments Act in some states) that simply states:
"Mr./Ms. X worked with us from [date] to [date] as [designation]."
The reason for termination need not be mentioned unless required for internal records or disciplinary proceeding.
Issue a relieving/service certificate mentioning only dates and designation, to avoid future disputes.
You can decline issuing an experience letter with performance comments, since the short tenure and misconduct do not warrant it.

In such a scenario as stated by you, the employee might have been on probation for a specific period, where no releiving / experience letter is required to be issued, recheck appointment letter.  

Thank you Vashista and Kalaiselvan for your prompt reply

You are welcome for your appreciations.

"They found out she display unacceptable or improper behaviour, Thy also has the recording of her misconduct and fired her immediately."

The statement is too vague and the action appears to be arbitrary.  If at all she was on probation and service liable to be terminated immediately, such action ought to have been a simplicitor without any imputation as to wrongdoing on her part. 

Needless to state, the experience/relieving letter need  to be  simple without any imputations.