Regarding the accent as a general rule in Sardinian it shouldn't be marked when it goes on the penultimate syllable of words such as in this case. Therefore "S'Alighèra" is incorrect. Furthermore, the accent is acute as it always is in Sardinian. The use of the the grave accent is just a copy of the Italian norm which mainly uses grave accents. If used for Sardinian it differs from pronunciation. Supposedly this error is made made because it is not easy to write acute accents on keyboards with Italian format or simply as a copy of the Italian written form. In other words it is a transliteration of Sardinian to Italian.