She's never said that; maybe you're mistaken.

OR

She's never said that. Maybe you're mistaken.

Whatever other languages permit, you cannot in English combine two sentences into a compound sentence with the use of a comma only. That is the fault called a comma splice.

English sure is weird!

Yes, English is probably the most promiscuous of languages in terms of its readiness to borrow foreign words and declare them English, a trend that has continued at least since the Viking and Norman invasions.

At the same time, the native grammar, as with most other languages, is very conservative and changes very slowly.

Meanwhile, rules of spelling, which have been very malleable in other languages — Russian, German and Lithuanian, among others, have all had significant spelling reforms within the last hundred years — tend to be ossified in English, due at least in part to the powerful and baleful effect of early dictionary compilers, as well as to a desire to preserve some mutual intelligibility among texts written by speakers of quite differently pronounced regional Englishes.

Punctuation has some variability, but English punctuators tend to break into two camps: people who demand the use of the serial comma before the "and" in a list of three or more items (also known as the Harvard comma or the Oxford comma) and those who eschew the use of the serial comma except to resolve ambiguity.

English is probably the only major language that has NOT had a conscious spelling reform... ever, I think? (Russian? Check. German? Check. French? Check. Spanish? Check. Portuguese? Check. Chinese? Check. Japanese? Check (I think?). Italian? Hmm, don't know.)
This does look like you're subtly trolling the entire world, given that English is the lingua franca of today. :)

> Japanese? Check (I think?).

http://en.wikipedia.org/wiki/Ja..._script_reform

The biggest change took place in 1946.
http://en.wikipedia.org/wiki/Modern_kana_usage
http://en.wikipedia.org/wiki/T%C5%8Dy%C5%8D_kanji

Man, that must have been massive!
I wonder how many people were utterly baffled by the whole major writing restructuring thing. It looks to have been quite drastic.
(Curiously, Russia/USSR hardly experienced any such problem because the intellectuals who vehemently disagreed with the 1918 reform were generally the ones who went into emigration, while most of the population at the time were peasants who did not particularly care. It was a simple enough change anyway, mostly getting rid of homophonous letters and several cases of traditional spelling inconsistent with pronunciation.)

I guess that the reform of kana (phonetic symbols) was less problematic. We can now basically just spell as we pronounce. The historical kana was really complicated and hard to learn, even though it's actually more logical in some ways (and more beautiful, as some argue).

The reforms of kanji apparently caused much more trouble. One major problem we have now is the inconsistency between the kanji inside and outside the "list". When they made a list of 1850 kanji in 1946, forms of some of the kanji have been simplified (e.g. 壽→寿, 鑄→鋳). Though people were supposed to refrain from using kanji outside the list, they kept using them, some in traditional forms, some in unofficial simplified forms (e.g. 濤→涛, 疇→畴, 躊→踌). In 1981, the government officially allowed to use kanji outside the list, but they didn't made any guidelines concerning their forms. Then, in 2000, they declared that it's desirable to print kanji outside the list in traditional forms. This means we're now supposed to use 寿 and 鋳, but 濤, 疇 and 躊. And they are all kanji we actually use. There are a lot of pairs like this. You need to know them if you really want to master Japanese. This is a history that almost no Japanese know.

If you're interested, here ([#852585]) are some more related comments I wrote before.

My suggestion would be to go with this one.

She's never said that. Maybe you're mistaken.

Or, drop the "has" if it matches the other sentences.

She never said that. Maybe you're mistaken.