So my child is still Rear facing

But one of our family members has her 2.5 year old daughter in a booster seat. I’ve shared things on Facebook to kind of indirectly get her to change her daughters seat (her daughter Is smaller than my March baby). I am not usually one to get involved in how anyone parents their child but GEESH. I am like having an anxiety attack trying to figure out if I should mention it to her, and if so, how do I go about it…I know most peoples thoughts are “not your kid” but what if she just truly doesn’t know. 😓