Is your daughter seeing any specialists ie ot, pt speech and language?
Have they given you any indication as to whether your daughter is on the autistic spectrum? Delayed speech and difficulties with social communication are parts of the diagnositic criteria for autism. Does she lack imagination, play games in a 'scripted' way, or try to always control the game. Does she show any feelings of isolation or is she quite happy to pay on her own. Does she has siblings? If so how do they play together.
Are there any sensory issues. Is she okay having her hair combed/washed. Does she have to have tags removed from clothes. Does she appear deaf or cover her ears at certain noises. Is she clumsy. Is she fussy with food or does she put non-food items in her mouth.
Does she appear to have any rigid routines of ways of thinking eg. only happy if things are done in the same sequence with the same outcome. If you have to put away her toys or turn off the TV does she have a tantrum. Does she have tantrums in general.
Does she repeat TV dialogue or things she has seen in adverts or on DVDs. Does she appear not to understand what you say. Does she repeat back to you questions you have asked her.
Is there any other behaviour you feel is 'odd'.
Is she at school yet? Whether at nursery or school how is she coping in that environment?
Whereabouts are you UK or USA?
If you can answer some of the above it will help to give you more specific advise.