Katie Holmes will do "whatever it takes" to win sole custody of her daughter.

The 33-year-old actress filed for divorce from estranged husband Tom Cruise last week and she is determined to be become the primary carer of the couple's six-year-old girl, Suri, as she doesn't want to be relegated to a "secondary role" in the youngster's life.

Sources say she has seen how Tom's second wife, Nicole Kidman, has been cut out of the lives of her children with the 'Rock of Ages' actor, Isabella, 19, and 17-year-old Connor, and Katie will not let that happen to her.

An insider close to Katie - who was wary of Suri being raised as a devout Scientologist like Tom, Isabella and Connor - said: "Bella and Connor aren't that close to Nicole, and Katie is determined that she won't be cut out of Suri's life. Bella and Connor are devoted to their father and Scientology, and Katie saw this firsthand, and this is one of the reasons she filed for sole custody. Katie will not be relegated to a secondary role in her daughter's life, period, and she is prepared to fight Tom in court. Katie isn't going to back down, and she will do whatever it takes to ensure that she raises Suri herself."

The former 'Dawson's Creek' star filed for divorce in New York as the courts there are more likely to grant one parent sole custody.

However, Tom is set to file a response in California and is determined to get joint custody of Suri.

The couple married in November 2006.