I think adoption center give child for some time to the adopting family to spend some time if she is saying words that mean she is not mute at least. For her age sentences is also right but kid's from orphanage usually have different environment so may be lagging in speech, social interaction but with proper warmth,love care they may come in main stream like a children's from good happy family. Also hearing evaluation if possible get it done. You will have to meet her frequently to find out the problem. Usually all basic test like CBC,
thyroid hormone,
HIv,Hbsag,VDRL, Mantoux test and X-ray chest for T.B.
Better visit some pediatrician nearby tell your concern he will suggest you for investigation,he can see the child also,if you bring the child to him