Olive, in your case it will depend on whether you have had chickenpox before, or if you have had the chickenpox vaccine. I guess the easiest way to explain it is to explain how your immune system works. When you are exposed to a disease (like chickenpox) your body's immune system identifies the disease and creates antibodies to attack that disease. This is the same as what happens when you are given a vaccine as the vaccines are made to be so similar to the disease itself that the same antibodies that are produced in response to the vaccine would work to kill the actual disease. Once this process has occurred, your immune system has a "memory" so that if you are exposed to that disease again, your immune system will recognise the disease straight away and produce those antibodies in bulk to fight off the disease. It's a bit more tricky when it comes to some diseases like colds and flus that modify pretty quickly and create different strains. In that case you immune system doesn't recognise it as the same disease and has to basically create new antibodies from scratch.

Ok, so that's what is happening in you when you are exposed. When it comes to breastmilk and feeding, basically, the antibodies that have been created by your immune system over your lifetime are present in your breastmilk. These are transferred to your baby, and then if they are exposed to a disease that you have antibodies for, your baby will also have some of those antibodies and their immune system will recognise the disease and start fighting it straight away (the same way your own body would).

In your case with the chickenpox, if you have antibodies against it, then you have probably passed some of those antibodies on to your DD2. If you have not had chickenpox before (or the vaccine), you will have no antibodies against it and your immune system will have to respond to it from scratch if you have actually caught the disease. For chickenpox, the incubation period is anywhere from 10 to 21 days after exposure to the virus. That means that it can take up to 21 days for the spots and rash to appear. The infectious period is from 2 days before the rash appears (so you can be contagious and not know you even have chickenpox) until all the spots are dry.

The good news is that if you have been infected with the virus, then your body will start producing antibodies and these will get passed onto your DD2. This means that her immune system will be getting a head start to fight chickenpox if she catches it.

Hope that helps