First think, What is capital?
Capital is total networth of a person. Networth is increased by increasing income. Capital increase or decrease every year based on whether person made a loss or profit.
If you are filing for first time, then bring opening capital as much as you can justify.
First take age of person. If she is 25 year old and earning or consider earnings for last 5 years.
If she has not filed IT returns in earlier year then consider income below taxable limit for each year. by considering income of last 5 years, you can increasing opening capital.