2 year old really nervous around other kids

Hi all, wondering if any of you have had this experience with your kids. I would love advice for helping navigate this and also positive stories about your barnacle baby/ sensitive/ shy kids doing well at childcare. Whole story below, thanks for any and all responses, and sorry this is so long but I want to give full context.

My 2 year old (just turned two, bday was yesterday!) is very nervous around other kids, especially in groups it seems. She has been home with us and our nanny full time since birth, so I suspect that is part of it as well as just being her personality.

She has always had very obvious, if not extreme, separation anxiety, especially with me (her mom). I had to go back to work at 14 weeks. I wfh and had a nanny who she ABSOLUTELY hated. Screamed the ENTIRE time she was away from me, just could not deal. it was the worst 3 months of my life. People told me she wouldn't care at that age, but she absolutely did and in a big way. Once we got a new nanny (my niece and her cousin who moved into our house) when baby was 6 months, it got a lot better. She did very well and has been since then. But she's always been anti being touched or held by anyone outside of me, dad, and nanny... including my extended family who live out of state. Also pretty possessive of me... she has cried because I've hugged my sister in front of her and also says "no no no no" if my and my husband touch/hold hands/kiss in front of her. She does well with her Dad, but always prefers me. He does bedtime with her every other night and handles child care Monday and Friday, she loves him but will always choose me if there's an option.

Also of note: When we go to the library, playground or social gatherings, she is not one of those kids that runs off. She's very cautious and will stay by my side like glue. She's very clearly interested in watching other kids play, and I know that is a type of play so i haven't been super stressed about that. that's who she is, she wants to watch first and take her time.

But now she is 2, and niece is moving out and moving on. It's time to start childcare. Because of her sensitivity we are doing half day montessori. (I'm lucky and grateful I have this option as my husband has a super flexible job working for himself, so he will be able to handle afternoons until im done working. and i may be able to hire some afternoon help to fill the gaps).

We start next week. I am a freaking mess of anxiety about this. I was feeling really good about it as she seemed to do really well during our visits to the school. But this past weekend we went on vacation with a bunch of my friends and their kids, and it was AWFUL.

It started off okay but at one point a toddler her age took a blackberry from her plate and she lost it. Never recovered. The whole weekend any time another kid even came near her she panicked. "Up up up up" would beg me to pick her up and then say "Inside" or "Outside" wherever we were indicating just "get me the hell out of here." She even told me she was nervous by literally saying "\[kids name\] Nervous!" She was even afraid of the 7 month old baby! She spent the whole weekend just demanding to be held, refusing to even acknowledge the other kids. The only time she seemed to relax was when the other kids weren't around. Overall she did well with the other adults and spoke to them and wasn't shy with them. (She even let my best friend hold her in her lap for a bit!) It was just the kids.

To be fair, it was a lot of driving and she was in a new place and there were a lot of other kids (8 total), many of whom are opposite from her and very rambunctious. She has done pretty well in other situations... If kids come close to her on the playground she gets really nervous. But we went to a birthday party recently where she actually WENT IN the bouncehouse. Demanded i come with her, but still. And she made a little friend at the park the other day and played super nicely. But still, it was just really hard to see her struggle with the other kids this weekend, especially when there were two other kids her age there who did great with it. Just ran around and had a ball.

So IDK im really just worried: Is this abnormal? Can toddlers have social anxiety and what do you even do about that? Is she going to be able to handle school? Do i need to consider occupational therapy or something? It seems like she needs the exposure of school but what if she just can't handle it? I NEED childcare of some kind and the only reason i was able to do the nanny for so long is bc it was my niece. Will she grow out of this?

I've just never met a kid like her- none of my nephews or friends have kids that behave this way. So again if you've made it this far, thank you. Any and all advice welcome.