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Oh poo-ey, poor Lucy

Ds does not have such a strong reaction, but he can't have milk products either, as they make him seriously constipated. If it's any consolation to you, I also had this when I was a baby but I outgrew it and have no problems now (am sitting here with some toffee ice-cream just to prove it to you

). Perhaps Lucy will do the same thing?
Just FYI, the substitutes we use are - rice milk (with added extra calcium) / soya yoghurt (tastes awful

, but ds loves it) / some horrible cheese substitute that ds likes.
Is it the lactose in cow's milk that she can't take? I tried ds on goat's milk thinking this would help, but it turns out this also has lactose in it, and had the same effect

. If I were you, I'd keep giving the things like the crackers if they don't seem to bother her. It's make her diet really limited if you didn't (not to mention your life very hard), and maybe she will be building up her tolerance that way.
BTW, if it has such a violent reaction, I'd call that an allergy