Reese Witherspoon had to ''grow up really fast'' when she became a parent.

The 'Big Little Lies' star was just 23 when she gave birth to daughter Ava - who she has with ex-husband Ryan Phillippe - and admitted it completely changed her life.

She said: ''I had to grow up really fast, and figure out what woman I wanted to be for my daughter.''

Despite winning praise for her role in 1999's 'Election', Reese - who as well as Ava, 20, also has Deacon, 16, with Ryan and Tennessee, seven, with current husband Jim Toth - struggled to get another job afterwards as studio bosses saw her as being ''repellent'' like her character and she recalled being ordered to ''dress sexy'' in order to be cast again.

She told The Hollywood Reporter: ''My manager finally called and said, 'You've got to go meet with the studio head because he will not approve you. He thinks you really are your character from Election and that you're repellent.' And then I was told to dress sexy.

''And you're 23, you have a baby at home, you need the money and you're being told that by people who know what they're doing.

''It's funny to think of all the things we were told to do back then because now you're thinking, 'Oh God, if somebody told my daughter to do that, she'd be like, I really hope you're joking.' ''

Reese, now 43, persevered and eventually landed her huge role as Elle Woods in 'Legally Blonde', though it required a number of awkward meetings with executives.

She said: ''I remember a room full of men who were asking me questions about being a coed and being in a sorority, even though I had dropped out of college four years earlier and I have never been inside a sorority house.''

And after winning praise for the role, Reese was inundated with offers - and didn't know what to do.

She admitted: ''I was so used to being underestimated that when I was somehow accepted, I didn't know how to look at material.

''I didn't know how to make decisions and I didn't know what I wanted to say.''