Not sure if there is a rule for it, and too lazy to look it up. My main concern is that the constant shifting back and forth breaks me out of the narrative as a reader. That is probably the strongest reason for keeping it in a consistent past tense. Plus, my head starts to hurt when I start thinking of "Okay, so this part is still currently in existence in this form and that part is a general truth about life, but then is this part still going on according to the continuity we hope to establish later on? And when IS Seledra telling this story anyway? Is she an older woman looking back on her life, or is she telling this three weeks from now or what?"

Makes my head hurt. I'll probably have to check a few novels written in past tense to see how this is handled.