The girl group are rallying around the singer - who went to rehab to be treated for depression and alcohol and sleeping pill addictions in 2011 after splitting from fiancé Tom Crane - to make sure she is recovering properly.
A source close to the group - which also includes Cheryl Cole, Nadine Coyle, Nicola Roberts and Kimberley Walsh - said: ''The girls are really looking after her. Sarah has put a lot of effort into her recovery and the band want to be fully behind her if she feels low.
''The girls have tried to make sure Sarah spends night son her own doing yoga and relaxation techniques before bed, so she can sleep without resorting to pills again.''
The source said Cheryl, in particular, has been fussing over Sarah ''like a mother'' and doing her best to make sure she stays in constant contact with her family.
The friend added to heat magazine: ''Sarah is a very passionate person and gets very easily swept up in excitement, and Cheryl's been fussing around her like a hen. She's in constant contact with Sarah's aunties and mum, because Cheryl's very family orientated.''