Why doesn't my cat know her own sister?

I have had these cats for 12 years and they are very close. Their names are Pebbles and Smokey. Yesterday, I got smokey groomed. She had a bath and got a trim. She looks kind of different and she smells really good. Now Pebbles keeps hissing at Smokey and wont go near her. I'm worried that she might think I replaced smokey with another cat. Is it possible that she doesn't recognize her own sister?