Ha! Tell her that my 15 month old has at least 4 feeds a day still...and he's a solid little fella, who might have solids twice a day if he feels like it, otherwise, it's booby and porridge for brekky, booby and 'scraps' (one mouthful here and there) for the rest of the day!
You know yourself. My next child may not want to feed this often at this age, so I'm just going with his flow I'm getting comments here and there, and I just say (with a shrug of the shoulders) "He loves his booby". Or I'll be feeding him somewhere and someone will ask "How old is he again?", because they are trying to reconcile what the stereotype is of breastfeeding age 'appropriateness' with what they are seeing.
When it comes down to it, YOU are his mother, not the other people with opinions