Christa actually rehearsed just what she should say if she got someone with truesight! Of if she didn't, since grabbing someone with it to ask her later if she'd lied was a pretty obvious thing for them to do.
She does not, actually, intend to tell him everything. The group that rescued her was well-intentioned, she thinks, and did, in fact, rescue her. She's just decided that rescuing Alard is more important than being rescued. Aire can just portal her off somewhere if the Lord Commander does decide to get blackmaily about it. But she does tell him everything that might be important for keeping people safe; that's what he might ask if she did later, she thinks. And she makes sure not to lie, that's obvious enough not to be worth thinking about, really.
She goes over her and Alard's date, although not in detail. And what happened after. How she knew Yui was suffering because of her use of telepathy earlier in the day to distract it during a stealthcraft exercise, and how she decided that made it her responsibility to, um, relieve Yui's urges. Alard felt it wasn't, but it was her fault Yui was uncomfortable in the first place, so it just made sense that she should help.
And then she fell asleep, and woke up somewhere else.
Kidnapping was maybe a poor way to phrase it? The person who grabbed her didn't ask permission, but she was, um, unconscious at the time, and they probably couldn't have woken her up if they'd tried, she was, um, tired. After the whole thing with Yui. And they were nice, and she's a telepath so she knows they weren't being dishonest about it. But, um, they thought Alard had made Yui rape her, which really makes the whole "grabbing her suddenly without stopping to explain" make a lot more sense.
Eventually she was told what was going on, that people thought she'd been eaten and raped by Yui. And from how they were talking she could tell the person who'd grabbed her also thought the whole rape thing. Then she decided to go out and make sure that everyone knew that actually Yui and Alard were innocent. She didn't think they'd let her go, they were worried about her safety, and their thoughts made it seem like they wouldn't believe her if she explained what actually happened, so she said she had to go to the bathroom and just left while they weren't paying attention.
Christa has a terrible sense of direction, so when she says she couldn't figure out how to get back there if she tried, she isn't actually lying.