Is C.G. unavailable as a witness when she failed to return to trial?

Defendant has not challenged the trial court's finding that C.G. became unavailable as a witness when she failed to return to trial. Under section 240, subdivision (a)(5), a declarant is unavailable when he or she is " '[a]bsent from the hearing and the proponent of his or her statement has exercised reasonable diligence but has been unable to procure his or her attendance by the court's process.' " "The term '[r]easonable diligence, often called "due diligence" in case law, " 'connotes persevering application, untiring efforts in good earnest, efforts of a substantial character.' " ' [Citation.] Considerations relevant to the due diligence inquiry 'include the timeliness of the search, the importance of the proffered testimony, and whether leads of the witness's possible location were competently explored.' [Citation.]" (People v. Herrera (2010) 49 Cal.4th 613, 622.)