18 month old speech

I have an 18 month old that is a second child. She says mama dada ow mine and try’s to say a lot of words that don’t quite make the full word but she gets part of it. She went for her 18 month check up and the doctor suggested coming back in 90 days to see if she progressed. She understands everything we talk about and do but she’s reluctant to say the words we ask her to say. Any suggestions/opinion?