Well I don't really feel like I can conclusively say what race Alex is, but I don't find the idea of her being a Latino to be completely unreasonable. The show is set in California where there is a large population of Latinos. There is also the issue of how she had feelings of jealousy towards Britney when she found out that Britney could speak Spanish. I would imagine that if she was a Latino that couldn't speak Spanish that would really get under her skin.
I also think that it's worth entertaining the possibility that she's Algerian. The show was made by French people and there is a notable Algerian minority in France due to the countries' proximity to each other and their shared history. It would wouldn't surprise me if the first nationality that a French creative team thought of when they decided to make a brown character was Algerian.
Regardless, don't take anything I say too seriously. I'm not the biggest fan of the show, I just like cute girls in skin-tight catsuits.