I will preface this by saying this is my own opinion and a possible scenario. After reading that Gianni, Sal and Ilona were indeed involved with drugs (heroin, Xanax), when it was vehemently denied by everyone at first, is it possible that Christina wasn't planning on leaving the apartment? She has a known connection (which we can't sleuth, so I won't say). It's not terribly unheard of for after hours parties to continue on partying. Could everyone in the apartment that night who wanted something give her some money and another party-goer who was wanting to leave walked her back to the garage where a sale would take place or she would drive to the sale? Said connection would know she had $$$$ on her from everyone at the party. The drug connect and herself would be somewhat known to one another in a general, peripheral kind of way and thus the sense of trust to voluntarily get into a car or meet up alone.
If that theory is simply to add a prior motive for her to have intended to get into EAs car at all, even if it could be proven to be true, it still wouldn't really change the rest of the story.
We're stuck with the simple fact that the DNA and blood of CM was found IN THE TRUNK of EA. As boring as it is to some, all by itself that presence of a large quantity of DNA and blood of hers in his trunk eliminates tons of other alternatives. When he left the garage at 3;58, so did she (in the same vehicle), and she wouldn't have ever been IN HIS TRUNK willingly or for her welfare. There's your abduction. Maybe a murder too.
In addition, if there had been some sort of semi-benign tale of how she happened to be in his car, EA would have undoubtedly offered that explanation long ago, in addition to telling where he left her and what else happened, in order to keep from such a serious charge of kidnapping and perhaps murder. His failure to say anything like that at any time truly speaks volumes.