If anyone knows, please spoil me as to what Veronica's ending slide should have been for the path I took (details below), because I didn't get one for her (maybe it is supposed to be that way). I am replaying but I want to do things differently this time, I already checked the Fallout Wiki and couldn't find out her ending that way.

Sided with the NCR, McNamara in charge of BoS and allied with NCR at Hoover Dam, and I didn't do Veronica's personal quest.

The wiki does have endings. http://fallout.wikia.com/wiki/Fallout:_New_Vegas_endings

If you just want this one without potential spoilage of others, I think it would be this: "Hoping to lead the Mojave Brotherhood down a new path, Veronica sought to learn from the thriving cultures of the desert. Absent a firm solution, Veronica's expression of frustration with Brotherhood leadership would lead to her banishment. She ended her days a wandering tinker."

Not doing Veronica's quest is the reason you didn't get her slide. The condition for this particular ending is missing, and it seems logical if things progress for her without any intervention from the Courier. The only other ending that doesn't involve finishing her quest is if she dies in your service.

Thank you, that's just what I wanted to know. I didn't think she'd have a good ending given that I didn't do her quest that time. (Was looking at Veronica's page on the Wiki, didn't realise there was a separate one for the endings, I think I'll avoid that until I've seen a few different outcomes from playing the game!)

I really wonder what's the best ending for her, none of them seems really good.
In my first party, i told her to stay in the BOS, with the BOS alive, i get the ending where she seems to become half crazy spending all her time in the BOS library (the ending n°6 in the new vegas endings page). Maybe the ending n°3 is better ?