My question is: can my french national client with 2 children claim IS? She is still married to her french national husband but they separated in 2005 due to domestic violence. She can claim JSA (IB) as a former worker but is there ANY way she can claim income support? She had to give up her last job due to child care problems...

She has been in the UK since 2001, was supported by her husband until 2005/6 when she worked, then claimed income support in 2007 and then found work in 2008.

Thank you!

Separated spouses are still family members of their partners and can derive R2R for IS as a single parent from their partner. So you need to investigate status of husband - is he a worker or former worker who has kept worker status?
Problem in these cases is often lack of evidence of partner's current/ previous status, but if you have a NINO of partner you can ask the DWP to trace for evidence of NI contributions paid or any other evidence which it may be more reasonable for them to have than your client ( Kerr vs Department for Social Justice ).