My suggestion is to keep her away from predominantly hispanic communities. I came to NYC (Park Slope, Brooklyn) when i was only 12 years old. I was sent to a bilingual Jr. HS which was fun b/c I had spanish speaking friends and then I went on to a bilingual HS for two years until i realized that I was not adjusting, I WAS GETTING COMFORTABLE and thats not always a good thing since by that time, i had been in the U.S. for about 4 years and my English was horrible. I transfered to a non-bilingual school and god, did i really need to catch up. Now i had no other choice for communitating except for English. It improved dramatically. Now i could have a conversation, know what ppl where talking about, understanding their ways, their behavior and every confusion just cleared up. I also didnt have to always walk 4 blocks to my spanish speaking friends when i could just chat w/ my next door neighbor...nice. Introducing her to some hispanics is very good. I'm sure she'll have a few question for them, but dont put her in a enviroment that she'll feel that she does not have to improve her communicational skills and to let her understand that although spanish is a beautiful language, english is essential. Also, you may take her out to latin clubs, bars, restaurants. Let her make frequent calls to her relatives in DR (she wont get off the phone for the first few weeks but that'll wear off) and dont wait more than a year b4 u travel back 2 DR.
About culture.... listen.. its not like dominicans dont know who the New York Yankees are... we are very familiar w/ the american culture, however, this is not to say that she'll understand everything (culture) when she lives among Americans. Explain this to her (this comes from personal experience), Let her know that not everyone is as polite as in the DR so that she doesnt feel bad when she greets ppl and gets no replies and that ppl are not always willing to help her when the groceries she carries are too heavy. That everynow and then, she's going to have doors landing at her face when she expected some one to hold it open for her.... It takes time, but she'll be fine.
--I should publish this book--