I don't think your fears sound ridiculous, yoyo.
I don't have any experience of early puberty, but if dd1's classmates are anything to go by, I would be surprised if your dd is the only girl in the class to be developing by Y5. Quite a few girls in dd1's Y5 class have the beginnings of boobs; I know two of them have started their periods, and there may well be others who have kept it quiet. The girls seem to be dealing with it in quite a mature way, although dd did come home recently giggling about one girl who announced while changing for PE, "I have hair under my arms" and then proceeded to prance around showing everyone. But the others were laughing with her rather than at her, IYSWIM. I would have thought that as long as the girls aren't being forced to have communal showers, your dd shouldn't be any more exposed on a school trip than getting changed for school PE or swimming.
I can see that you might be extra keen to protect your dd because she's developing so early, but at some point all girls are going to encounter other people making nasty remarks about their physical development (or lack thereof) and will have to deal with it somehow. Might it perhaps be worth helping your dd1 find strategies to cope with possible reactions from others rather than trying to protect her from it?
Although my dd isn't developing yet, she has also been teased about her body, in her case because she has very hairy legs. While I find it upsetting that she has to deal with that, I've concentrated on getting across the message that everybody has things about their body that they don't like, and that you can either waste your life getting paranoid about it, or make the best of it and get on with having a life. Humour has helped too: when she came home with a story about some particularly obnoxious (and very overweight) girl saying to her 'Eeer, yuk, you've got legs like a gorilla" my immediate reaction was, "Well ** isn't exactly a supermodel herself, is she?" which dd1 for some reason found incredibly amusing, and I've since heard her reusing that line to other people.
I think it might be worth trying to sort out how you feel about letting your dd1 go, because it does become more of an issue in the Y5/Y6 age groups as the world opens up a bit more to them. My dd1 has had all sorts of other problems of her own around being very perfectionist, finding it difficult to cope with criticism or failure and learning how to persevere, which have arisen partly from her personality and partly from being in a class where she's been very underdemanded academically (as I know your dd1 has been). Sending her on trips and activities away from the family environment has been a big part of our strategy for building up her confidence and encouraging her to tackle new and difficult things, and it has made an enormous difference to her over the past couple of years -- she's much more relaxed, more confident and flexible, and has much better social skills, with adults and other children.
hth