While I am very sad she won't be continuing the series, I completely understand why she doesn't want to. Much as we'd like to believe we'd love to see her own personal flare one the series, people would be looking for PTerry in them, and possibly grow bitter toward Rhianna for not being able to resurrect her father. Moreover, I imagine she wants what she puts out, in any medium, to be hers. Regardless of how much part she had in writing the Discworld novels with her father, I imagine she doesn't want to piggyback on PTerry's legacy. Even with her being the one writing the books, there would be very little room for her own voice.
And like she says about not wanting to write them without her father, I feel the experience would be hollow. It's one thing to ride a tandem bicycle by yourself, but it's entirely different to ride it alone when there used to be a second person.
I got my copy of Hogfather shortly before PTerry passed. I've seen the film adaptation, but it's the one Discworld book I've never actually read. I think I've been putting it off for reasons other than general lack of time.
Given that, I've read some of his non-Discworld books, but the bulk of them are entirely unknown to me, so even when I've read all of the Discworld novels through, I'll still have new adventures waiting for me in a sense.
Good on Rhianna for her choice. I hope she's found her peace and comfort, and I hope she finds as much inspiration in her future ventures.