Pretty sure it's not limited to that time frame, just to reputation, as I thought I recruited her much later than that point.
Viewing post in Can't seem to "flirt" with Maple
I was curious, so checked the code. you're right, you do have to start it while doing that quest. However, you only have to ask about faries, nothing more. The flirting can happen later, asking about fairies starts it out and that requires the mainquest, but the rest is independent of that. Everything requiring reputation can happen at any point after that, so just make sure to ask her about fairies when first tasked with finding a fairy.