Brit, 26, often has to be forbidden from leaving her home.
'We take it in turns to be with her and watch over her 24/7,' she explains.
'Britney is so anxious and so on-the-edge right now. She is incredibly keen to go out and doesn't understand when we tell her that it's not a good idea.'
Alli, 26, also reckons that Britney needs to quit showbiz to get well.
'She needs to rein herself in,' Alli tells the Daily Mirror. 'She needs to take a break from the limelight - from showbiz - and just concentrate on getting herself better, and being with her family.'
Britney's desire to be with sons Jayden James, 1, and Sean Preston, 2, is a key incentive in her bid to beat her demons.
'She desperately wants to be with her boys and be a great mother - and we want her to be as well,' says Alli. 'She just needs to have a break for as long as it takes until she's completely better. We are with her 100 per cent of the way.'
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