Janine, I say your little daughter already has a head start in school—if for no other reason than that you read to her! There is no better way to prepare a child for school than to read to him or her from infancy onward.
And your daughter is lucky to hear different languages during the period of life when her brain can properly distinguish among all the different sounds used in different languages. You are right that “they” say this type of exposure results in slightly later use of what is to be the major language. But it is interesting that most of the researchers who comprise the “they say” people live in America. Many Americans have trouble learning to speak a single language (English) well, whereas in Europe, the acquisition of four or five languages seems to be a snap!
I wouldn’t worry if, because of her attempts to understand more than one language, she is a little slow in speaking any of them.
Sometimes in multi-language families, a young child will appear to become confused and reduce the amount of talking in any language. Or she may possibly show hesitation or seem to block when starting to say something. If this happens to your little girl, concentrate mainly on one language for the time being, in your case French. But by the time she is 3 or so, I would move her gradually into English, the language she will presumably use in school and will need for communication with her peers.
Our parenting advice is given as suggestions only. We recommend you also consult your healthcare provider, and urge you to contact them immediately if your question is urgent or about a medical condition.