How to handle work friend’s sudden change in mood

background:
I’ve been at my new job for 6 months. I mostly work in an office with one other person (Ann) but recently our line manager (LM) has moved back into our office.

Ann and I have spent a lot of time together this last 6 months and I honestly can’t believe how well we get on. For the first time in a few years I feel like I have a best friend. We both suspect we have adhd and definitely have experienced mild issues socialising/taking things too personally with other people in our past. That’s relevant.

The lead up:
Ann has been working a lot and doesn’t have a lot of days off left. She’s not been happy for people going on summer holidays and has made comments to me all summer about wishing they’d stop going on about it/rubbing it in. Ann recently had her long-awaited two weeks off (the only holiday days she has left until Christmas) and I thought she’d feel refreshed and happier after it but she’s come back with a bit of an attitude.

While she was away, LM and I both realised we needed to book the same days off at the end of the month because of school holidays. LM said she would book in less work those days since it would only be Ann in the office. LM told me on Ann’s first day back in the office she’d had to have a word with Ann for making comments about people’s leave but didn’t go into more detail.

Due to Ann working away from the office the rest of the week I ended up not working with her until Friday. She texted to ask if I was coming in 5 minutes after our usual start time and I realised she must not have known that I’d booked all of Thursday and the first hour of Friday off for family reasons. I explained I’d be in after this appointment.

The issue:
When I got in, LM was working away from the office and Ann had put on some weird, depressing music I’d never heard before (we normally listen to upbeat, inoffensive pop stuff in the office). She was really quiet, verging on silent treatment. Normally she talks to the point of distraction so this is abnormal. There was an oppressive mood in the office so I just tried to ignore it and get on with my work. After an hour of silence she asked out the blue, “do you know when you and LM are on leave together I’ll be in the office on my own for 4 days?” I said, “yes, but LM is booking less work those days to accommodate that”. She went back to not speaking to me. Later, we had this exchange:
Ann: was LM in the office yesterday or still travelling?
Me: I don’t know, I was off
Ann: Do you mean you booked leave?!
Me: yeah.
More silence.

Later, she did make conversation twice and although her tone seemed tense somehow, I’d hoped she was over whatever it was that was bothering her. There were still long stretches of silence though. At one point I was editing something (from an outside source) and I joked that it was written like Yoda wrote it and she snapped, “if you don’t like how it’s written, re-write it!” A while later I asked her advice on how she would re-word a particular line (by the same yoda-like author) and she snapped, “I wouldn’t”. By the end of the day I pretended I was in a rush to get home and ran out the office so I didn’t need to walk with her like we normally do.

I’m dreading going in on Monday. I hate confrontation, like may have an actual anxiety attack type of hate but I feel like I can’t go to LM about this without confronting Ann first. I feel like if I say anything she’ll act like she doesn’t know what I’m talking about. And if she breezes into the office like nothing happened, I don’t think I can go on being her friend like nothing’s happened. I feel like she intentionally ruined my entire weekend (and tarnished our friendship!) because she got a bee in her bonnet about me me and/or LM using leave and I don’t think that’s behaviour I can or should just let go because it’s not ok. It felt very manipulative. I guess I’m also worried that I was possibly just being overly sensitive that day though.

Sorry this was so long. Any advice on how to play it on Monday would be appreciated.