Natasha's handwriting, when she isn't paying careful attention to playing a role, would be very distinctive as well: the English script of someone whose first writing script was Cyrillic is hella different from someone whose first writing script was any of the writing styles taught in the US these days, and very hard for the person doing the writing to override. (I have yet to find a good scan-and-upload of the English language handwriting of someone whose first script was Cyrillic, but you can get a sense of some of what it would look like by image-searching the phrase "russian cursive makes me cry sometimes", heh. Take that and map it onto Latin-alphabet writing and it's very, very distinctive.) I have tried to reproduce what it looks like to show someone, but my Russian handwriting was never really very good -- I was much better at speaking the language than reading/writing it -- and the "really hard to override" goes both ways.
I will someday! Especially now that I can type more :D