To me, definitely a basenji mix. I have seen registered basenjis who are not square, 'curvy' topline. She is not as refined as a female basenji but that might be the mix showing up.
The howling noises are very basenji to me.
A few basenji characteristics she may/may not have:
Licks herself when wet, like a cat, does not have a doggy odor when wet, picks a particular time of day, and goes nuts, consistent with the time of day. Has a hard time controlling herself when a small critter, especially a rabbit is near.
Thinking she is part basenji will buy her a few 'oh well, that's the basenji part showing up' when she does something that a regular dog will get reprimanded for. With Lexi, roll up a newspaper and swat YOURSELF for not giving her a baseni proof environment!
Your life with Lexi will never be boring!