I would not step in as a parent, yet (if ever). I would see if your D can find other resources at the school to escalate too. Who does the advisor report to? Can she contact her school’s dean, or another mentor within the school? I think I would have her just keep trying people at the school until she gets some assistance.
Especially since your D is a senior and this is about her internship and future employment, my opinion is that this is hers to figure out. I understand that it is a hard and stressful situation for you both, and the threat of her not graduating is scary. And it is bad that her advisor isn’t calling her back. But IMO your D still has things to try, and it’s not your place, and very soon, she really won’t have the option of you stepping in.