Aww…

If she’s gravid, that would certainly cause her to be hissy. I’m a bit surprised that she hasn’t always been hissy. You may have lucked out and got one of the more rare ‘friendly’ lady veileds. Or, as she’s reached full maturity, her attitude has finally kicked in. I adore my girl Stella but is she isn’t trying to eat my fingers (must think they’re giant fat worms), then she’s trying to bite. When she was young, she was very sweet and never hissed or tried to bite.
Also, many will mistake a chameleon as being friendly because it willingly comes out to their hand, when the reality is they don’t like their enclosure and are taking any way they can to escape it. I know you’ve done a lot of work making your little Izzy’s home perfect. She may be so happy and content in it now, that she’s comfortable in letting her attitude out and not wanting to be bothered by a human.