Be VERY careful here.
Have you ever met her face to face?

Do some research on Ghana and scams. There is a common and well known scam going on. DO NOT send her any money.

Not nearly enough information.

She will need her own visa as there is no visa for the girlfriend of a US citizen. It will depend on her education and employment experience, plus she will need a US business to petition for her if she qualifies for the visa.