"She is very tall now."
现在她很高了 would be fine and also natural; 现在她很高 also would sound like her height is changing spontaneously. It is difficult to explain, but I think mostly it is because Chinese is heavily based on the context. If you mention 了, I can understand it as a state now (that she is tall) as a result evolved from a previous state (that she was not used to be tall); Without 了, simply 她很高 already means she is tall at such moment, and mentioning 现在 additionally hints that she was not tall just a while ago. This will be alright if you say 现在她的血压很高/Her blood pressure is (very) high now, because blood pressure may fluctuate within a short time, and the sentence just point out an instantaneous observation now.