Did the investigator specify what other evidence she needed, or was it just a general "more"? Many property damage offenses go unsolved because they are done at random. Pictures and estimates of damage are to be expected, and while they are necessary to prove up other elements of the offense, they do nothing to show the identity of the perpetrator. The texts go a long way in showing who did the damage, depending on the wording. When you originally met with the investigator, did she download the text messages off your phone, or take pictures of them? If she didn't do either of those things, you should do so yourself in order to preserve the evidence. You don't say how much the damage estimate is, but if it is a small amount (less than $50.00) this will be a Class C Misdemeanor, which is the equivalent of a traffic ticket, and the investigator may not think it is worth her time. The messier, personal aspects of the case, specifically the affair, may also figure into the investigator's analysis of the case and willingness to go forward. Unfortunately, you don't have a lot of other options in pursuing a criminal case. Like the other commenter said, the decision about whether or not to file charges ultimately lies with the police agency and the District Attorney's Office. You also have few options in terms of getting financial help to fix your car. Texas has a Crime Victim's Compensation Fund, but it is only for victims of violent crime. Keep pressing the investigator; call regularly, perhaps on a weekly basis. Be polite, but persistent. If you go ahead and get the damage fixed, KEEP THE RECEIPT! If you feel like you are being harassed by the ex girlfriend, keep a detailed log of all her contact with you and the words said. This should include dates and locations. Don't egg her on and don't initiate contact with her on your own. Keep your nose clean. If her contact with you doesn't diminish over the course of the next few months, try to file a harrassment complaint. If she threatens you or your husband at any point contact the police immediately because that is a much more serious issue. Good luck.
Criminal prosecution is a matter for the DA.
YOU can also file a civil suit and seek damages.
The above is not intended as legal advice. The response does not constitute the creation of an attorney client relationship as this forum does not provide for a confidential communication.
Often times police do not do what they need to do to make a case - especially when it seems to be "civil" or "family" issues. Be calm and ask the officer what else is needed. There may be something specific that you can easily provide. Otherwise, if the officer refuses to proceed further, ask for a superviser - but do this as a last step because it will make people mad and may not get you results.
Otherwise, you can file lawsuit against her in small claims court. This may not only get you restitution but also the "evidence" that the police seem to want you to chase.