You were originally a pre-med student so its reasonable to assume that you really wanted to work in healthcare in the first place. But, what do you really want, to become a nurse or to become a doctor? Even with the 2.5 GPA, if medicine is what you really want to do, at 24 you're still young enough to go back and do the pre med courses and raise your GPA high enough to compete for a spot in medical school. If you've already decided that you want to do CRNA instead, then it seems to me like you're in good shape because you've already done the biology, chemistry, and math courses, and all of those are required for the ADN.
Here is my recommended plan of action:
Do not apply directly to an ADN program right now. A 2.5 GPA is a 'C' average, and with nursing school admissions so severely competitive the odds are against your being selected for a spot, especially since you just recently graduated with a degree in an entirely different discipline. Instead, apply to the college as a pre-nursing major. Take microbiology with lab and a liberal arts course in the summer, and statistics and another liberal arts course in the fall. By the end of the year you will have completed all the pre-requisite science and math courses for nursing school, and hopefully, you will have selected some 'easy' liberal arts classes to boost up your GPA. An important thing to note is that if you are going to be working full-time while you are doing these classes it is not a good idea to do more than two classes at a time. Your goal is to get all 'A's because this is what's going to help your GPA.
At this point, start working on a very convincing essay about your reasons for wanting to become a nurse so that you can have it fine-tuned and ready to fire when you apply to nursing school. Not every nursing school requires this, but, believe me, it helps. Also, find out from the nursing schools that you intend to apply to about any additional requirements. If there is an entrance exam find out about the type of questions are on the exam and prepare yourself for that. The issue you'll likely face is being put on a waiting list once you get in.
The CRNA part of your plan can be set aside for now. Before you can apply to CRNA school you will first need to have your RN license and be working in critical care for at least a year. But, you haven't yet even begun nursing school so this is what I would concentrate on right now if I were you.
FYI, not every CRNA program requires that you have a BSN degree to apply. If you are an RN with a bachelors degree in another discipline some schools offer bridge classes that you can take. You should check out the CRNA forum for more info about this.
Good luck with your plans.