Found it:
'His charge sheet alleges he "unlawfully and by force took or carried away Sarah Everard against her will".' - it's from the Daily Mirror's account of court proceedings today. The fact it's in quotation marks suggests it's a direct transcription of the charge sheet. As a reminder, UK definition of kidnap is "to take by force or by fraud" - the fact the charge sheet specifically states she was taken "by force" seems to me to rule out that she was taken by fraud - ie, she wasn't coerced or tricked into getting into the car - she was physically forced into it.
This makes sense to me. He's a bulky, muscular guy, and she's a slight woman - he'd have no need to come up with some detailed plan about how to convince her to get in the car - much easier, and quicker, just to physically force her in there. As someone else has pointed out, it'd be over in seconds. As they say, the simplest explanations are usually the correct ones.
To me that fully answers the question of how she got in the car - he put her there.
Link:
Police officer accused of abducting and murdering Sarah Everard appears in court