Its hatrd to know what is right and wrong with so many different views and information out there....maybe ask her if she has a gut feeling something is wrong...thats the best way. Like the girls said is he showing signs of talking babbling, pointing, reaching grapsing etc? Some kids are slow walker and crawlers...my biys were fast crawlers but slw walkers and talkers but Ds1 is very normal now!
Hope she can get some info to put her mind at ease