Sorry no one has got back to you on this, I've only just recently returned from holiday and started catching up with the forum.

I think it could be a combination of all three of the factors you mentioned. She may be catching up with her feeding if she was taking less while she had croup, and if she still has a sore throat, she may be feeding for comfort as well - breastfeeding soothes a sore throat and breast milk is a good pain reliever.

As well, the flu vaccine can cause mild flu-like symptoms, so she may be comfort feeding for that reason as well.

Are things starting to settle down?