Basenjis are typically aggressive on leash...
And she is so right. My two are perfect angels running free, meeting and greeting a plethora of other canines in the woods, but approaching the carpark again, they go on leads. I do not trust motorists.
That is when they will snarl at dogs they have just been racing and chasing with ! It doesn't worry me because I know that, once loose again tomorrow, all will be sunshine and light.
I think she is feeling vulnerable being on a leash the whole time.