My tenant recently failed PCA and we lodged an appeal and applied for IS which was awarded. It is clearly stated on the form that she is a single person aged 33. When IS at reduced rate was paid because it included backdated payments it was a lump sum.
I however noticed that the amount of the award suggested that she had a dependant and IS were made aware that she had no dependants.

IS have now further reduced the award on the assumption that my tenant gets child benefit which she doesn't. she now has £28 pw to live on.

I am not sure whether to appeal the decision as there is the matter of a possible overpayment of IS as it now appears that when IB (IS) was paid it was on the basis that she was a lone parent.

She is estranged from former partner and dependant son lives with ex-partner, she is not sure whether he gets CB/CTC for him.

Even if she did get Child Benefit, it should only be taken into account as income if she had been getting Income Support with a child included since before 6th April 2004. I think you need to contact the Income Support section and find out why they are only paying her the £28. Could be deductions for other debts, perhaps even including an overpayment decision that she didn't know about/didn't appeal?