Yes, hope you must be having abortion report. 

- As per law, a complaint must be filed within a maximum period of 3 years from the date of cause of action , and in special circumstances it may be 7 years. 

- However, this limitation not applied in case of sexual assault i.e. rape type of heinous crimes 

- Your sister can file a complaint before the police for lodging an FIR against him , and if police not give positive response then file a complaint before the magistrate. 

- Further, if your sister not wanted to come into light , then this complaint can be filed by her father or you on her behalf. 

This is serios issue. Complaint will register but you will need medical report. 

1. Yes get the abortion report. 
2. However, abortion is not a proof of rape. It's just a proof of sexual encounter, may be consensual or not  
3. It's possible to complain to police, but would be very difficult to establish even a prima-facie case, solely on the basis of an abortion report. You have to produce other material...  Convincing Reason why it wasn't complained of at the first opportunity, the chronology of events, situation etc. 

1. There is no point in digging the grave where corps was buried 2 decades ago.

2.However for such offence there is no time limit but after so many years such allegation would be very hard to establish in court.

3. Due to long lapse of time it is better to forget this chapter.

There is gross delay in filing case of 15 years 

2) there is no police complaint filed of sexual assault 

3) you can file rape case but you have to explain in FIR as to why you were silent for 15 years 

4) it would be difficult to prove rape 

You don’t have the abortion report 

you have no evidence about alleged rape 

tou can file complaint t if you so desire 

You can file a case but it will be difficult to prove the same in court without evidence 

- Abortion report is not mandatory to lodge an FIR against the accused . 

- If she files a complaint before the police then police can arrange the same from the said doctor where the abortion was taking place. 

The delay to report the crime is the great disadvantage to her.

Her complaint may not even be entertained by the police at this belated stage.

This is not assault but a rape offence and very serious.

Does she have the abortion report ?

If yes, then she can approach the police with a complaint but remember that it is 15 years from that date till now hence the establishment of the crime or offence at this stage where there are no substantial evidences to prove may not be available, it is advisable that she better continue her life how she had been doing so far

In the absence of documentary evidences or any other evidence to prove your case which is an essential ingredient to entertain any criminal complaint, you may not get any support from law enforcing agency nor through court 

Hence you have to decide whether to run between courts and home without any  hope for the desired relief, you may decide the next course of action specially when she is married and living with her two children a peaceful life, do you want to create problem/ruin her peaceful married life at this stage

1. It is a criminal matter for which she shall have to first lodge a police complaint.

2. Police will enquire about the matter  and shall register FIR if they find prima facie evidence in the complaint.

3. The incidence has taken place before 15 years for which no evidence can be obtained by police or submitted by your sister.

4. It will be prudent on your part no to stir the matter any further in your own interest.

1. The is no evidence lying with you.

2. No doctor will remember that he had aborted your sister before 15 years.

3. Even the doctor deposes that she was aborted before 15 years, how shall you prove that that person had raped her?

4. I find no fruitful result in making a police complaint at this stage.

Try lodging a fir by approaching the local police. This will be tough as the incident is very old, and ideally it ought to have been reported long back.

If the local Police does not lodges your FIR, write to the Police higher ups. 

Dear client, For an offence whose punishment is greater than three years imprisonment, for example, rape, murder etc., the crimes can be reported even after three years of the action taking place.