01/27/2009 at 02:15 PM EST
It's been a rough start to 2009 for Kelly Osbourne. After being arrested
for allegedly slapping a journalist earlier this month, Sharon and Ozzy's daughter checked herself
into a Los Angeles rehab facility for a 30-day stay.
"Kelly's always struggled with addiction," a source tells PEOPLE about Osbourne, 24, who's previously been to rehab for painkiller addiction in 2004 and 2005.
The source goes on to say that Osbourne, who divides her time between London and L.A., is greatly influenced by where she's living – and that her lifestyle in London "is very bad for her."
"It's a very party atmosphere there," says the source. "[Kelly] just tends to get back into that rut when she's there since her friends are there, and she's just more comfortable there. The old party habits come back."
When Osbourne checked into treatment, her rep told PEOPLE that former reality star wanted "to address some personal issues."
Though he couldn't be reached for comment, Osbourne's boyfriend, London-based model Luke Worrell, seems to be a positive influence on Osbourne. "She's never been happier," says the source. "She's really found love with Luke."
For more on what triggered Kelly Osbourne's latest stint in rehab, pick up the new issue of PEOPLE, on newsstands Friday
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