I don't know about the tenses. I agree that the festival description should be put in past tense, because that's the tense that she's been using for her other narration. The other paragraph you mention (the description of the garden), however, isn't really part of the narrative, per se. It's a description of something that arguably still exists in that form in whatever present the narrator is speaking to us from. It's ongoing, not a point in time in the story, therefore I might consider it separate.

But then, I suppose I must put in a disclaimer here that my formal writing training is mostly in essay writing, not fiction*, so I really don't know what the "standard" is for this sort of thing. I can see switching to past tense just as a matter of remaining consistent.

Also, even if she switches to past tense, I'm not sure I'd have her do it to the "most difficult part of my job" line, because, again, presumably it's still a part of her job from when ever she's writing, and unlike the description of the garden, is also a generality.

*The only fiction writing class I ever took was utter shite. It really only taught me not to take creative writing at Joliet Junior College.