At 20 months we expect the child to speak a minimum of 15-20 words and speak in small broken sentences,but child intially develops receptive language i.e she understands most of the basic communicative language and follows most of the things we tell but expressive language development varies from child to child few Children speak well after joining play school, according to me if a child understands our language and follows commands it's only a matter of time before they start talking.
Next Steps
Try to talk to her in only one language initially and use regular language spoken normally in house because she hears that most of the time, don't teach language it comes naturally through regular conversation with her
Health Tips
Don't use baby language ,talk to her like you talk to others,try not to understand her sign language act dumb when they are signalling instead of talking this might propel them to speak..hope this info helps