"She needs to leave now."
Thanks for the explanation. I've been a Chinese speaker for over a decade and even studied the language formally at a Chinese university for two years (I'm simply doing Duo as a way of keeping my skills sharp now that I'm back in the US), and it just seems a little odd that I've never encountered 必须要 before.
Knowing that you know the language will make the explanation easier.
Think about this sentence: 人必须要有耐心，特别是要有信心。
Without 要 it would sound weird, so 要 is not always dispensable imo, and it's pretty natural here to use 必须要, however, I haven't studied grammar systematically (XD kind of sad to say that) to point out the grammatical reason behind. I think 要 appears because we say 要有，要做，要离开, so it's because it sticks to the verb and not much related to 必须. I would say the sentence is more 她|现在|必须|要离开 than 她|现在|必须要|离开.
Another example: 必须得想个办法。
If we want to add 要 in there, it won't be 必须要得想个办法, but rather 必须得要想个办法, so the 要 stays next to the verb. Adding a sense of emergency/must-be-done undertone to the verb.