Verb to be: ser / estar .. everything depends on the situation.. in this case, if you translate "she's very happy" you could use "ella está muy feliz" when you know that "ella está muy feliz" that she's living the moment and you know that she "está" very happy ... If you attribute to happy person you should use "Ella es feliz" from verb "ser"
I have also had this problem in another form: If I use Lopez or any other word that has a counter part in English I run into problems. If I use an accent mark over the "o" the spell checker the spell checker marks it as an error, if I don't use the accent mark the program chides me for leaving it out. Very confusing. I have found that generally, if some English speaker uses accent marks for words that in other languages like Lopez (when writing) it is considered to be an affectation. If an English speaker says the word as accented they are often viewed as showing. off and are often ridiculed. So, it seems you can't win either way.