There are so many parts to your request:
Are teens self-involved? Usually. They have so much going on externally and internally. Your daughter has a big heart and responds when asked. Good for her! Sounds like you've done a great job so far, Mom.
How did all the aunties and grandparents get her number? If she gave it to them, then they probably know she values their contact even if she doesn't reply right away. Not every contact requires immediate response, and 24 hours is your own arbitrary time limit, not hers or theirs.
If YOU gave her number to extended family, then I dearly hope it was for safety reasons only. If not, you're probably too much in her business.
If you gave her the phone with certain conditions attached, then you should take it away if she doesn't meet those conditions. However, I'd carefully consider the reasons SHE may need the phone, and make sure your conditions are within the scope of her legitimate needs. If not, you may want to rewrite the "rules" so they make good sense to her AND to you.
It may be useful to find out what your daughter's ideas of good etiquette actually are. She may have a pretty good handle on what's necessary, and what's gratuitous fluff. My mom, for example, gifts my inbox with "cute" forwarded messages. I can not and do not respond to every one. My idea of good-enough etiquette there is to comment positively on the few that I do enjoy, and ignore the rest.
As a daughter who was constantly coerced, manipulated, and shamed by my mother well into my first marriage, I lean toward supporting and guiding the personality children are born with. Most kids will ultimately be more responsible when given some freedom to learn for themselves what works and what doesn't. I did this with my daughter, who was so much fun as a child, and is now an admirable professional woman and sensitive human being. And she's doing the same with her son, a charming and radiant little boy. He's sef-centered, as is normal for a child, AND he has many moments of dazzling thougthfulness, which we all celebrate.
Teaching by example is usually very effective in the long run, in my observation. Nagging or demanding might get results, but doesn't leave a child enough room to respond with their own inner resources, and so teaches less effectively.