If it is an ablative absoulte it shouldn't have a finite verb in it, it should have a participle. It seems "tutela" is the nominative singular "I the protected one" and valui is indeed the past tense of valeo: "was strong" or "was safe". It may be a technical term from Roman law, or from some obscure poem. Either way I bet neither Ms. Dupree nor her tattoo artist were great Latinists.