There are two things that I wish were explored more in doujins:
1) Meiling being Flandre's caretaker like is often played with in one-off pictures. And
2) The period before the SDM came to Gensokyo, after Meiling is hired, but before Sakuya shows up. I like to imagine Meiling taking on a sort of Brock Sampson role, doing a mix of housekeeping, bodyguarding, the occasional chasing off an angry group of humans, and dealing with Vampire hunters.