“She´s happy” vs “She's happy” vs “She’s happy” vs ...?

"She's happy" uses unicode character U+0027, which is an apostrophe.

"She´s happy" uses unicode character U+00B4, which is an acute accent.

The first is correct, the second is wrong.

There are other alternatives to U+0027 as an apostrophe:-

There is unicode character, U+02BC [᾿], which is the modifier letter apostrophe and that could also be used appropriately.

It should be noted that the Unicode committee (controversially) recommend using character U+2019 [’] for an apostrophe (which is the right single quotation mark).

The reason that using the acute accent and right single quotation mark characters is a problem, is that machine parsing of the text (such as autoformatting) can misinterpret the intended character and produce erroneous output. (We see something similar here when people use the grave accent (U+0060 [`]) along with the acute accent as quotation marks and it renders the word between in code markup.)