You were sinful for not returning it on time.Try to find her again. If you absolutely can’t, give this money in Muslim charity in her name. On the day of judgement, you will find out whether this was sufficient or she will take from your good deeds until she has enough.

Dear brother,my question is that in 2001 i borrowed 200 pounds from someone but i never return the money even though she was asking her money back.Now,after learning about debt,i want to return the money but i cant find the person as shes from another country,it`s very difficult to find he,what shall i do?