Learn French: C'est une informaticienne brésilienne. - She is a Brazilian computer scientist.

Because the profession (informaticienne) is modified by an adjective (brésilienne). If we just stated her profession without the adjective, we would drop the article and use elle est: Elle est informaticienne. But as soon as we add an article (une) and a modifying adjective, French requires c'est.

How do the masculine forms of the noun and adjective change to create this feminine sentence?

Both the masculine noun informaticien and the masculine adjective brésilien end in -en. To make them feminine, you double the n and add an e, resulting in informaticienne and brésilienne.

Why is brésilienne placed after the profession instead of before it?

In French, adjectives describing nationality, geographic origin, or religion always come directly after the noun they modify.

Does informaticienne only mean 'computer scientist'?

While it often translates to 'computer scientist', it is actually a broader term for anyone working in Information Technology (IT). Depending on her specific job, it could also mean software engineer, IT specialist, or programmer.