Why wouldn't she? Flan is just appreciating the flowers, which is what the Flowers want, even if she picked them. The 'kills anyone who so much as looks at her flowers' thing is fanon hyperbole, as is opposing picking flowers - canon Yuuka patronizes the Flower shop of the Human Village, which requires both of those to be false.
NinjaPope said:
On the other hand, Flan is probably one of the few who doesn't have to fear Yuuka.
If you mean via the fact that Flan canonically isn't quite all there upstairs and therefore doesn't have the proper fight or flight response, sure. If you mean power levels, you're pretty much way off. Flan isn't actually very high on the totem pole of Power Levels in Gensokyo, and Yuuka basically sits on the top of it via the various statements that Zun has made (only of Gensokyo, other places is a different story although he's still extremely vague on that, but let's not get into the entire 2hu-verse powerlevels argument because that's an internet firestorm waiting to happen).
