Es würde mich interessieren, ob es das Wort "muslima" auf im Englischen gibt.

yes, spelled muslimah, though. One look in a dictionary should suffice:
http://www.oxforddictionaries.com/us/definiti...
Muslimah
pronunciation: /ˈmʊzlɪmə/ /ˈmʌzlɪmə/
noun
(Especially among Muslims) a Muslim woman.

That might be a BE spelling, with the H.

'Especially among Muslims' is probably an understatement; I would imagine only among Muslims.

'Muslim woman' is the term for a general audience.

I don't see why "Muslima(h)" would be only among Muslims. We say "squaw" or "señorita," too, for example, without those words being limited to Native Americans and Mexicans respectively.

I know the word exists. I also know a lot of muslim women (not exaggerating here... way more than 2, for example).
In fact, I have never heard one refer to herself in English as a muslima(h), always as a muslim woman.

...unscientific, I know :) :)

I'm neither a Muslim nor a woman, and I can't say I know "a lot of Muslims," male or female, but I read a lot. That's no more a "scientific" approach than RES-can's, but there seem to be some incidents of Muslim women calling themselves "Muslimas" that can even be found on the net:

http://www.whatisislamabout.com/muslim/muslima/
What is a Muslima ?
A Muslima is a Muslim woman. Not all Muslim women refer to themselves as Muslimas; those who do tend to be younger, and sometimes more socially aware. The use of the term “Muslima” is akin to the use of words like “Latina,” which is used to describe a woman of Latin origin. Ultimately, the decision to refer to oneself as a Muslima is a personal choice; more conservative Muslims tend not to use it.

Ein Schlaglicht:

In den Nürnberger Nachrichten, der führenden Regionalzeitung in Nordbayern, wurde das Wort "Muslima" in den letzten 8 Jahren 54-mal verwendet.

Re #7: As compared to what? 'Schildkröte'? 'Japanerin'? 'Bier'? What's your point?

Re #6: I have no doubt that there are (some) Muslim women who use the term; I'm just skeptical that any significant number of non-Muslims use it (in English).

#7 soll aufzeigen, dass das Wort "Muslima" in D nicht nur von Muslimen gebraucht wird. "only among Muslims" gilt also nicht für D.
Der Duden führt es übrigens auch auf.

What, because most white people don't use it it's not a valid word in the English language? How long did it take for hijab, niqab or burka to become readilyunderstood by non-Muslims? Seems to me those are mostly English-speaking Muslim women who refer to themselves as Muslima(h)s. It's also listed in several dictionaries such as the one in #2, and there a Wikipedia entry mention the word:
http://en.wikipedia.org/wiki/Muslim
A female Muslim is sometimes called a "Muslimah".

Compare, for instance, "Latina":
http://www.merriam-webster.com/dictionary/latina
First Known Use: 1983

That would mean that until 32 years ago, no one (supposedly) knew what a Latina was.

Re #9: But that wasn't the question; the question was whether it's (commonly) used in English. And our answer was, no, not really outside the Muslim community. For example, no, you would probaby not see it at all in a general-audience newspaper.

And thanks for ruining my attempt at editing myself.

Ditto.

--> probably

... unlike hijab or burqa, but possibly not unlike niqab. Some words assimilate to the wider culture faster than others.

For example, no, you would probably not see it at all in a general-audience newspaper. - There's a lot of words you wouldn't see in a general audience newspaper, like the "n" word, for instance, or any number of swear words. But more than 14 million google hits for "Muslimah" give us a pretty good idea of the word's popularity in general, I think.

I think it's not much used in BE, at least. I've only ever seen it in German.