My professor once came to my office and she proposed to me a well-posed research question: it was a theorem to prove that she was extremely happy to see and that would be a nice research question. After some months I went to her office claiming I solved it. She read it and highlighted some points that were not clear to her. I made the proof clean and neat, even generalizing it more than what she wanted. At the very end, she said: "well, I see you solve it. Nice!" and all ended up like this.
My question is: I basically did everything on that problem and my advisor "just" (even if I am grateful for this) made me aware of the research topic and basically read the first draft pointing out some things to explain a bit more. Now she seems not to be interested in publishing the paper, while it is for sure worth of publication since this is what she told me at the beginning. Hence, I am willing to do the job on my own. The question is: should I write it as a solo author, just with some thanks in the intro page or is it more polite to put her as co-author (even if, honestly, she did no more than what I told above)?