It sounds like she is making the situation worse and worse by not facing up to it. She is embarrassing and inconveniencing the DA and wasting the court's time. The DA is reasonably upset.
I'm not an attorney, but could she not simply refuse to testify? Can't your attorney discuss having the case against you dropped?
The material witness warrant is a tool to haul in and possibly detain a key witness in the DA's case. The DA could just want to talk to her, or the DA is making sure that she will be present for the next court date. The police can look for her at home or work and arrest her.
If she did lie to the DA, then she might want to consider getting an attorney as well. She needs to face the situation and avoid antagonizing the DA further. She needs to talk to an attorney to figure out how much trouble she might be in, how likely she is to be charged, and how to resolve the situation before it gets worse. It can't be your public defender of course. The attorney will likely advise that she turn herself in as well, unless the warrant can be dropped.
If your public defender isn't already negotiating with the DA to try to have the case against you dropped, then I think you need a new attorney. You need to figure out how to afford one now, or you might be paying later in permanent repercussions to your life.

