Lily probably writes because the bar for entry is probably the lowest among the arts. All you need is a writing implement and something to write on, and nowadays computers are so ubiquitous anybody can smash on a keyboard and vomit it online. This is why you get hundreds of thousands of fanfics written by teenage girls; no barrier for entry.
But the skill ceiling is very high, and that huge gulf between people who are just cutting their teeth on the craft because they were inspired by One Direction (or, well, Harry Potter) and people who have honed their skills but are still inspired by One Direction (or Harry Potter) is vast. Lily probably keeps writing because it's easy, the younger members of fandoms reward self-indulgence, and her skill level is
just high enough that those same younger readers won't have the literary experience to see or fully process how bad it actually is.
"Rowling's belief that changing the status quo itself is bad" The entire setting is built upon satirizing the wonderment of the Wizarding World, that with each book the Wizards look more and more backwards with how they're both visually and philosophically stuck in the past.
This is 100% true in the body of the books but kind of falls apart in the epilogue, where it seems that nothing has changed despite the systemic problems of the Wizarding World and that's what a lot of people ultimately walked away with, at least as far as those problems are concerned. I think the issue is that Rowling had the epilogue drafted years and years ahead of the end of the series and while it was obviously changed somewhat (the series originally ended with the word 'scar', for instance, which is obviously no longer the case) she was ultimately married to that scene.
Narratively it's a good button on the lives of the characters, but I see why people can get aggravated.
That said, Lily is obviously just parroting bad-faith arguments from people who now hate Rowling and only re-read the books to prove she's a fascist (not that I like them or anything, baka).
The House Elves thing is pretty funny, given the standard complaints about them.
The actual issue with the House Elves is a little more complex than even being an enslaved species-- they're based on British folklore about fae that would secretly assist humans (oftentimes in ways the humans didn't appreciate) and who could only be dismissed by thanking them for their endeavors by leaving a gift (in the House Elves' case, the gifting of clothes). This is taken to a logical conclusion by having the wizards be aware of such magical beings, and have thus figured out how to 'employ' their services. House Elves in the book do by nature desire to serve humans because of these origins, but this was also taken to its logical conclusion by showing shitty people taking advantage and abusing them.
The joke about SPEW wasn't that House Elf rights were incorrect (this is illustrated both by Dobby's treatment, Sirius' abuse of Kreacher, and the EXPLICITLY UNSETTLING statue in the Ministry showing all the other magical races, including House Elves, effectively worshiping the wizards standing above them). It's that Hermione decided she knew the best interests of a group she was advocating for without even
talking to them and ignored that, no, the sentient creatures did not appreciate her going White Man's Burden for them.
Most people who twist Rowling's character like to use this as her advocating slavery (as you said) despite obviously showing how fucked up the system is, so yes, it's
very funny to see that Lily decides that dealing with the problem is both (1) too hard and (2) would deprive Harry of ready-made servants who can do basically anything and he simply has
no choice but to accept their kindness there's just
nothing he can do about it, he totally would though, but he can't, so he just has to respect them and probably let them solve all his problems.
