At the beginning of her message, Aleksandra was explaining some of the changes that have occured in the Croatian language that differentiate it from modern literary Serbian. Phrases utilizing "da+present tense" of a verb to indicate an infinitive are avoided as "Serbisms." Certain words are likewise avoided as Serbisms as well (tisuća/hiljada, hleb/kruh, bližnica/komšija, sretan/srećan.) Finally, there are spelling and pronunciation differences between literary Serbian and literary Croatian. The former is based on "ekavian" dialect and the latter "ijekavian." For example, "river" in Serbian is "reka" but "rijeka" in Croatian (other examples: "milk"- mleka/mlijeka, "time" vreme/vrijeme, "where"- gde/gdje).
Everyday folk though(unless they are really politically conscious) speak in the manner of the region they were brought up in, regardless of their ethnic background. For example, Serbs from Krajina (the mountainous region bordering Bosnia-Hercegovina in Croatia) speak primarily "ijekavian," so do the Serbs from Bosnia until one gets closer to Serbia proper. In Vojvodina (North Serbia), and Slavonija (eastern Croatia), Croatians (like some of my family) would use some "ekavian" words and constructions.
One should aslo mention the other dialects that did not really play a part in the formation of modern Serbian and Croatian. There is a third dialect found along the coast, "ikavian/čakavian" that is spoken by both Serbs and Croats (words are written with an "i"- "Vrime," "Gdi", "Mlika"). It is also found to a certain extent among Catholic Bunjevac communities in Vojvodina (refugess from the Turks who settled there hundreds of years ago).
Around Zagreb, there is found the "kajkavian" dialect (which I have a hard time understanding- it sounds like Slovenian to me), and in the south of Serbia there is the "Torlakian" which has affinities with neighboring Bulgarian and Macedonian dialects.
That's probably more than you wanted to know, so I apologize for the long-winded digression.