"The brief onomastic formula of this Šethre Sentina (Ta 1.202) neither presents us with ulterior data nor relevance to our knowledge of the gens, which despite the nomen of an ethnic type, boasts exclusively Tarquinian attestation. The support is uncertain."Frankly I'm not sure what the problem is in etymologizing this name. Firstly Sentina can be securely formed from the combination of praenomen Sentiie (TLE 113: Senties 'of Sentiie') plus the suffix of appurtenance -na. This praenomen is in turn attributable to the attested Latin name Sentius.
While I haven't read this directly, I would presume that the Latin name in turn formed, as many Latin cognomina do, from a descriptive adjective. In this case, sentus 'thorny, rough, rugged' seems like a decent match. So I see nothing Etruscan in this name aside from its highly productive suffix.
 I've translated this from the Italian: "La brevissima formula onomastica di questo Šethre Sentina (Ta 1.202) non apporta dati ulteriori nè rilevanti alla nostra conoscenza della gens, che malgrado il nomen di tipo etnico, vanta attestazioni esclusivamente tarquiniesi. Il supporto è incerto."