How can i extend her stay because she is 3 months pregnant and I dont want her to go back now.
I would very much doubt it. She has already had a 6-month visitor visa, and in order to get an extension in the UK it would have to be truly exceptional. Being 3 months pregnant is hardly likely to be in that category.
Why did she come here on a visitor visa, rather than as your dependant?
By the way, posting a reminder message after merely 67 minutes is not appreciated. Everyone here posts freely and is not compelled to reply. Seeing that reminder I almost decided to leave my reply until the morning, on principle. Your constant posts could explain why no one else has replied.