Feel free to disagree with me - this is my own experience and opinion
There are 2 types of submissive women you'll meet on any fetish site, those who will swoon and those who seem cold. The ones who swoon, who are enamored by your eloquent dominance in the first few messages, they are caught in the dream you've so aptly created for them. It's exactly what they want. Mystery and lack of control is quite intoxicating, but eventually the smoke clears and all that's left are the mirrors. It may be after only a few hours, or it may be after weeks of talking. You might even meet in person. Inevitably, no matter what kind of person you are behind it all, she wakes up as if from a dream. She feels silly and self conscious, even though she's the one who put herself in such a position. Even if you've set up the perfect fantasy, it can all come crashing down.
Then the ones who are seem cold or distant, despite your warmest attention. The ones who don't respond past your first few messages, or draw out the "get to know you" phase. Here's the thing about being a woman, it's terrifying. Every man you meet is potentially a threat to your safety, it's ingrained in the minds of every woman you've ever met. Online, it's that much worse no matter how long you spend getting to know each other, there's always the underlying fear. Now add submission into the mix. The expectation of submission when she's already so disadvantaged is almost absurd. There lies the never ending dilemma, craving the sweet and beautiful release of submission while understanding the horrifying risks. Sometimes it just isn't worth it.
It may seem as though she's leading you on or being dishonest. It's often difficult to see past the disappointment of someone you're interested in turning you down. It feels like a betrayal because the bond you make feels like a promise, especially since bdsm relationships often involve promises. Here is the thing you must remember, it's quite likely that you are not her priority. There are exceptions, some really do want to dedicate their entire lives to the service of someone else (and there's nothing wrong with that, the very thought of it is intoxicating), but chances are she has some kind of goals and dreams of her own that mean you cannot have all of her attention. Try not to fault her too much for changing her mind, she may have every intention of staying under your spell until the moment she wakes.