There isn’t enough information here to know if the treatment program is subject to the HIPAA privacy rule or even to figure out what kind of treatment program this is. Those things make a difference.
There is nothing, however, that you can do to get her records. She will need to pursue that. I suggest she start asking the facility if it has a particular form it uses for records requests. If it does, she should get that and fill it out. Most medical facilities and treatment centers want to get the request in writing and won’t give out records simply on a verbal request. If the facility does not have a form, the she needs the address of the office where the records are kept and send a letter politely asking for the records. She might cite the federal Department of Health and Human Services (HHS) regulation under the Health Insurance Portability and Accountability Act (HIPAA) that requires medical facilities that are subject to HIPAA to release to the patient his/her medical records (other than certain psychotherapy notes). This regulation is found at 45 CFR § 164.524(a). That might be enough to do the trick for her. Sometimes just being able to cite a law in her favor will be enough to get the facility to act and get off their butts and get the info to her.
If that doesn’t work then she will likely need a subpoena or court order to get the records. A subpoena may only be issued when it is needed to get information/evidence to be used in pending litigation in which it is relevant. She wants to use it to aid in her criminal defense in County B. Her lawyer as an officer of the court may be able to issue a subpoena herself to get the records. If the facility is subject to HIPAA, however, it might insist on a subpoena/order from the judge. In that case, the attorney may file the appropriate motion with the court to get that. As your girlfriend is represented by a lawyer it must be her lawyer that issues the subpoena or files a motion with the judge. Your girlfriend cannot do that herself (and certainly you cannot either since you have nothing to do with this).
If the facility is subject to HIPAA and refuses to comply with the written request for a copy of her records then your girlfriend could file a complaint in the appropriate federal or state court to force the facility to comply with the regulation and give her the records. Her public defender won’t be able to do that, probably, since it is outside the scope of her representation in the criminal case. Your girlfriend would likely need to find a lawyer familiar with litigating matters like this. Trying to do it pro se is not recommended. So doing this is not likely to be cheap. The other problem with this route is that this sort of litigation can take many months to resolve if the facility really wants to fight it.
Your girlfriend is free to dump her public defender and hire her own lawyer to handle the criminal case and do what is needed to get the records, if she can scrape up the money to pay for that. If she really thinks the lawyer is not representing her competently (and that’s different from whether she’s doing a top notch job) she might see if the public defender’s office will assign her a new attorney. No guarantee that any replacement lawyer would be better, though. There isn’t enough information to tell whether your girlfriend is getting a competent defense or not.
In the end it might not matter much. Even if she is pursuing her treatment plan it might not move the DA in County B to soften his stand on her case. Nothing requires the DA to give her a nice deal here. The DA can press for the max if he wants. Of course, there is no guarantee the court would give the DA the kind of sentence the DA seeks. Your girlfriend apparently has stolen things from at least two places (maybe more) and criminals who commit multiple crimes get less sympathy from prosecutors and judges for obvious reasons. Even if the court does not impose the max sentence if your girlfriend is convicted your girlfriend may well be looking at some time in jail or prison from this. She’ll have to be prepared for that possibility.

