Thanks for the replies.
She's breastfed, and has never shown any kind of reaction to anything I've eaten the whole time I've been feeding her. And I've eaten exactly what I normally would have done, including a whole range of fruit, and things like tomato which I know some people avoid - the only thing I've changed is to only have the very, very occasional glass of wine. So I don't think my diet has affected her.
Bizarrely, she'd been having kiwi for a while and not had any problems with it. And she's had apple before and not been bothered by it. Which is why I thought she couldn't be genuinely allergic. She is also teething at the moment, which someone told me stimulates more stomach acid because of all the drool. So I am wondering whether she might have been OK with mildly acidic things to start with, but now the combination of acid from fruit + extra stomach acid is proving too much. Does that sound possible? Or is the teething thing a complete red herring?!
She is absolutely fine with banana, pear and mango. No idea if any of them contain fructose, though.
Any suggestions on sensible things to read in this area ... I'm someone who really like to feel like I've read up on a subject to be able to make sensible decisions and I know absolutely nothing about nutrition, even in general, never mind for babies! So I feel at a bit of a loss. I don't even know what contains fructuse, or what foods are acidic! Any good books/websites anyone can recommend.