It sounds like your daughter is on the verge of ready, but is probably not quite there yet. Here's one of several sites that gives some great "readiness" checklists: http://www.parentingscience.com/toilet-training-readiness...
There are stories on this site of toddlers trained by 18 months. There are also stories of such young kids regressing once the initial push is relaxed. Most children will train somewhere between 2.5 and 3.5 years, with quite a few finally succeeding even later than that (most of them will be boys).
So your daughter is on the early end of training success. It's probably a mixed blessing that she's the latest in her age group; a sense of failure or frustration tends to prolong the process, but if the emotional aspect is handled well, she may find motivation in the success her classmates have demonstrated.
But basically, a child will be fully trained at whatever age they have reached the degree of physical, emotional and cognitive maturity required; if your daughter reaches that readiness at, say, 29 months, she'll be able to succeed at 29 months, no matter how long she's been "in training." Keep it positive and cheerful, express your confident that she'll figure it out when she's ready, and try to guard against discouragement and frustration (for both you AND your daughter).