What she is recommending doesn't even make sense. What could you possibly put in the bottle that would be better than breast milk, and if weaning is the goal, how does drinking from a bottle constitute being weaned? I can see how drinking from a bottle would make parent-led weaning easier later (bottles can just disappear, but your breasts can't), but you don't plan to wean this way, and at any rate, it doesn't seem worth switching to a bottle just for this purpose.
The advice you've gotten so far seems good. I would probably say something like, "Thank you for being concerned about it, but we're comfortable with what we're doing."