If I was innocent I'd for sure wanna take the stand but the prosecution would tear you to shreds and just nothing good can come of it really. Don't think you can ever really prepare yourself for that type of questioning.
As far as the specific investigation period, there's some sort of rule which means even if they know she likely did more before child A, they can only look at a certain time frame for this trial if I remember correctly.
I'm not sure on the attempted murder charges-does this mean it's reached the threshold that they think she knew she could cause death? Or does it not work like that? Because she's a nurse, I think she knows what will kill a child and the attempts were not actual attempts to kill those times but more like GBH or equivalent? Not that it matters I guess, she still needs to go down for all of it (if guilty-I say that every time just because trial is not over yet). Just speaking purely from a motive point of view on the attempts.