Next week's EastEnders episodes see Tanya Jessop (Jo Joyner) confide in Lauren over her sad secret, explaining that she has been diagnosed with cervical cancer.
Jossa told Inside Soap of Lauren's reaction: "Immediately, there's a change in her - with Tanya so sick, Lauren has to grow up. You'd expect her to dive into the drink again or something like that, but she's right there for Tanya from the minute she finds out what's going on."
She continued: "Tanya is still convinced she'll be fine, but then she finds out that the cancer has begun to spread. Tanya's really vulnerable at that point and it's Lauren who's saying, 'We're going to fix this and everything will be fine'.
"She's there for her mum the whole time - shopping, cooking, cleaning, looking after Abi and Oscar. She really wants to help Tanya and actually enjoys the responsibility."
EastEnders fans will see Tanya tell Lauren the truth next Tuesday at 7.30pm on BBC One.
> EastEnders spoiler: Jodie discovers Darren has cheated on her
> EastEnders spoiler: Darren bids a sad farewell to the Square
> EastEnders spoiler: Yusef stoops to a chilling new low
> EastEnders spoiler: Tanya tells Lauren her cancer has spread
> EastEnders Tanya secret will be discovered, says Jo Joyner
> Read more EastEnders spoilers and news
Watch Lauren Branning's EastEnders character trail below: