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Thanks all, I got her from a woman whose cat had accidentally got pregnant, so not a breeder exactly. Mother cat then disappeared leaving her 4, five week old kittens to fend for themselves! :(
She's not wiped her bum on the carpet again, so maybe it was just a one off?! Think I'll give the vet a call and see what they say re.worming tabs.
I guess as long as food is on offer so she can help herself, and she's very active, she can't be starving.
Thanks again for the advice everyone, it's been 4 years since my last kitten but they are SO different!!