I would first apologise for continuously blaming her. I think it’s very believable and very possible it was her friend

I know you did it was hard to read her, but did she seem ashamed, or afraid? If so, that could explain 2 things imo. Either she had sex, or she fucked something. What that something is, we may never know. Maybe she is embarrassed because she fucked a banana or maybe she didn’t want you to know she fucked a dildo. Idk that’s for you to decide, especially since you obviously know if you guys are very open about sex and your needs.

I would believe her if it were me, but I would also be more skeptical, and I think you should be as well. No matter the reason, it’s sketchy. I would personally be more worried about were she is and shit like that