The kitten CANNOT catch Leukaemia from the owner of a positive cat, so please don't worry. I work with positive & negative cats and only have to take basic hygiene precautions. @It is a contagious disease, but can only be transmitted via direct contact, and even then its not a huge risk unless the cats are fighting, mating or grooming each other. I don't think you have anything to worry about here, by all means get the kitten tested, but if she is positive, she had the disease before coming into contact with this lady.
Oh, and bathing the kitten would not do anything even if she had caught it.