"They have taken her for ..." indicates an ongoing state of things. "They take her for ..." indicates that this is the current state of things, and says nothing about the past. Either could work well. "They have been taking her ..." in my view does not work as well, and surely is not as commonly used, but would not be incorrect.
"They haven’t even had to say it" is not incorrect, but it took me a moment to understand the intended meaning.
The sentence could be rephrased as:
Even though they didn't say it, it was clear because I have seen their attitudes towards her by their behavior.
or if they did in fact say it as :
Even if I hadn't heard them say it, it was clear because I have seen their attitudes towards her by their behavior.
"after their behavior" would not be correct unless it is referring to some specific behavior that happened previously, and that was mentioned earlier in the statement. "in their behavior" could by used instead of "by their behavior".