Yes i would say she worked very fast indeed considering the time she had to complete this work and there were many cards to be done in a short space of time? i do not accept that she had any help doing this as what we have learned about Pixie she was a very independent lady that really only lived by her own standards in that time, it was really hard for any woman in those times being independent to get by when not being married she really only had herself to rely on and she also wanted to be recognized as a professional artist?
While I agree that she probably did the coloring herself, I somewhat disagree with the reasoning. While most accounts depict her as a plucky, independent woman ahead of her time, it was still of her time, and those times weren't as backward as one might think. Women did earn a living doing all sorts of things, although this would get a big boost a few years later, when WWWI began. Feminism in those days was very different than today, even the suffrage movement was only just starting to take off.
Secondly, there's nothing to indicate she wouldn't allow anyone to help her, as aside from how big the job was, it wasn't a "special" job about which she would be passionate. On the contrary, it is surprising she did as well as she did, considering the restraints. As an artist for hire, she would do whatever was ordered, and if Waite asked for b&w that's what he would get. Furthermore, as a veteran illustrator, she would understand printing processes, which would mean Rider would have the final say over the amount of colors used, plates, etc.
Still, I think she probably did the colors herself.