So the most important factor in selecting a PhD program is finding a mentor whose research interests match yours. It's really better to go to a lower ranked school with a good mentor then to go to a good school with a bad match. I generally tell people to stay away from online programs because generally they are unfunded (an I don't think anyone should pay for an informatics or nursing PhD) and most seem to just be for people who want the credential to teach, not really do research, which I am gathering is what you want to do. Though I can understand your not wanting to move with kids. It's been a while since I applied so I'm not sure if there have been improvements in online offerings.
Another thing you could do is attend the American Medical Informatics Association (AMIA.org) in October. That will make it easy to identify people who are doing research that your interested in and possibly meet them (giving you a leg up in the admissions process). Also, almost all the biomedical informatics programs have booths there so you can find out about applying. If you want you can also PM and I can give you more detailed information about my particular program if you're interested.