How do I find out if a female in Accra Ghana is a scammer?

The odds are seriously stacked against you.
Rule of thumb, enjoy yourself until they ask for Cash then RUN for the hills.

If she asks for money she IS

The sum of money is one thing, passport and visa to most places are under 300 USD total. There is no requirement medical forms, and no requirement for travel allowance (money in the bank)

If she is 10 times a pretty as a girl in the US is, that would date you, expect that also. if she is in love with you after 3 weeks of chatting.

Most real dating happens from people who know people, and someone in US or your national will introduce you.