She downplays what happened

She didn't want to admit her blunder but even if she wanted to hide it, she still felt horny.
Maybe in common circumstances she could hide and endure till the aphrodisiacal effect was over, or she could deal with it on her own... but here?
If they kept hunting then her aroused state may lead to distractions, and distractions may lead to giving their opponents some openings to take advantage of.

If that were to pass... well, things could end up very badly.
Therefore, after they were done collecting their loot and walked off, Mei took the chance to pull Ren aside in order to come out with it and seek his help... well, more like seek his D.

"Uh? Is something wrong?" he asked, unsure about why his girl was showing a bashful albeit remorseful look.

"I... earlier..." how should she say it? I got distracted and one of those dirty monkeys stuck his tongue down my throat?
She wanted to come out with it, but now that she was about to she didn't know how to. After fidgeting for a while, she decided to downplay what happened "While i was fighting the babooches, well, there were many of them and i was worried about you and..."

Ren was getting a bad feeling about this but didn't interrupt her, letting her explain "...well, in a moment of distraction, one of them managed to brush his lips on mine..." her voice got tiniery by the word, but he could still hear what she said and rage towards the monkeys immediately flared up. Those damned babooches! How dare they try to kiss my Mei!

He felt he should have stabbed their corpses a few more times, but now they were already a distance away and it wouldn't be worth it to go back just to vent his anger... though maybe he would, if she had told him the offender didn't just brush his lips but gave her the frenching of her life.

She could feel his rage and was worried he'd be disgusted with her for allowing a beast to taste her lips, but her worries were unfounded as he immediately repressed his feeling and hugged her "It must have been terrible... sorry, it's all my fault, it's because i'm not strong enough that you had to distract them despite your injuries..." Mei felt guilty as the experience hadn't been as terrible as he was making it out to be... to be precise her mind did categorize it as disgusting and her reason refused to accept how good it made her feel, blaming their aphrodisiacal saliva for that.

"Uhm..." she tried to get to the point, trying to come up with an excuse that wouldn't make him doubt just how deep was that kiss "...while it was just a brush, it did leave some saliva on me and... well, their spit can get girls very horny" she put it in simple terms as she knew he was a simple guy... well, putting it nicely he was simple, to put it straighforwardly she knew he was an uneducated countryboy and was hoping to use his ignorance to make her excuse pass without him prying further.

She tried her luck, and it worked.
Ren previously heard about babooches and their aphrodisiac spit, but didn't know much about it... the effect was mild at best, but for all Ren's knew even ingesting a single drop could be troublesome.
Since he knew the outline but not the details, it was easy for Mei to fool him in thinking that just a little spit on her lips was enough to get her hot, though to give her argument further credibility she still added "It wasn't much but... well, better be safe than sorry, no? Since we don't know what we'll find out there, better work it out my body now..."

Her voice slowly turned more seductive as she said, making it look like she was using the aphrodisiac saliva as an excuse to get down and dirty with him, though once again it worked as all the anger towards the monkeys turned into lust for his woman, his manhood almost bursting from his pants at the thought of reminding Mei's body just who she belonged to...