Nuance refers to the subtle, often complex differences between a given situation and other, similar situations.
Individual dynamic is essentially used here as a synonym for relationship. The term feels a bit awkward to me, so I wouldn't necessarily use it. The notion is that relationships between people are constantly changing, so the subtle, complex differences may also change.
There isn't enough context here to be certain, but I expect previous sentences in the explanation attempted to impart advice in more-general terms. This subsequent sentence further advises that the matter is more complicated than the general terms, and that you must adjust based, depending on your circumstances.
Essentially, the sentence is warning that you may need to apply any previous statements differently, depending on the relationship you have with her.