Disclaimer- this is largely based on my own opinion, I just want to know if I should have a tactful word with the other mum or am just being a snob.
A girl I used to work with has a baby 3 weeks younger than mine so is now 2 and a half, she posts pictures of absolutely everything on Facebook and, no word of a lie, I have maybe seen 3-4 photos of him out of hundreds without a dummy. This kid CONSTANTLY has a dummy in his mouth; he's playing- dummy in the mouth, he's smiling- dummy in the mouth, he's sat in front of the TV- dummy in the mouth. I have no problem with dummies in general, they can be an absolute life saver for younger babies, mine had one but gave them up of her own accord at 10 months but my HV told me that a dummy should just be a last resort if they're upset as it can slow down speech and emotional development if you depend on them (because baby isn't expressing themselves and just being placated).
From what she's shared on FB it's quite obvious that he's behind on his speech for his age. WIBU to bring it up when I next see her and maybe suggest that they try cutting down on the dummy?