I normally take the cue from my kid. I don't offer the milk at home only when she (21 months too) ask for it. In school, they are offered the milk before nap and at tea break, normally I will inform the teacher it is fine if she wants to skip the milk should she is taking the solid food well. After one year old, milk is only a supplement to her diet as mentioned by Agnes. If she is eating well and having a well balanced and nutritious diet, can get all the nutrition that she needs from the food too.