You can say something, but it might not do any good, and her parents might not appreciate it much. Your patient might act out more than usual when she's not feeling well. You mention that the nurses were hanging blood products. Your patient might be more opinionated and stubborn than usual when her counts are low.
Adults understand the difference in the way their body feels when their counts are low, or they're developing a fever, or they're becoming septic... they may not understand which of these is happening, but they know something's wrong and are able to verbalize that. Pediatric patients can't. So, much like infants cry when they don't feel well, preschoolers react differently than usual. They may withdraw and become quiet, they may cry, or they may become obnoxious and loud. Your patient's father may understand that, and it could be that this is why he wasn't correcting his daughter; he may have seen this behavior from her before when she has been ill in the past.