How to tactfully say no to requests and opportunities

K.A. writes:

I had someone contact me for an interview series last year. She had a tight deadline, and I accommodated and got all the info + images to her despite being really busy with client work. She ended up scrapping the series and never published it. I was a little annoyed! Well, I just got an email from her wanting to set up another interview about the projects I’m working on… I don’t really have time and feel a little burned by our last interaction – I hate saying that, but it’s the truth! Any ideas on gentle ways to say no?!