Sweetie all i can offer is hugs and tell you that my step daughter was still needing a nap when she was 5.....she didn't LIKE it, but it certainly helped her sleep if we didn't let her sleep too late.
With your LO if she is old enough to understand I would INSIST that she has nap time every day (unless you are too busy of course)...she is allowed to be in bed and look at her books, but she must stay in bed for at least 40 minutes (to give her a chance for a nap if she can), and if nothing else she has some down time!
I know it's slightly different but if our 20 month old doesn't nap well during the day our night times usually have multiple night wakings, it obviously disturbs his sleep cycles that much!
As kids get older (actually all the way through) you can't make them sleep, all you can do is give them the opportunity to do so
Naps are so restorative and important, I would keep persisting if you are finding that her night sleeps are still suffering. Hopefully soon she won't need her nap during the day and her night sleep will extend and settle down
Sorry can't be more helpful, but big hugs to you
xxLizzie