Hello!
Here's a step by step guide of seeing Rhoslyn Good Ending.
It's probably full of spoilers, so watch out!

If you want to learn how to clear Rhoslyn route without the FULL guide,
try:
Not asking them what's wrong (Leave them alone)
Don't push them, UNLESS you're doing it in a friendly/funny matter
Don't be too cheesy early on, but show affection later on.
Be mean to other Fae, but don't harm the forest


Now below is the FULL guide

Occasionally there are fluff choices.
I've indicated fluff choices with "-----" .


Guide:

[Investigate]
"------"
Okay, then. Rhoslyn.
"------"
I heard that you're a him... or a her...
Sounds good.
Allow it
" got lost again
NEVER LEAVE!!
Go and talk to Rhoslyn
Don't ask
Hey
...Rig the sink to spray June
It wasn't you? I'm sorry
Huh. I guess you do.
"----"
[Give up]
Push Rhoslyn out of the forest line
Don't ask
There's nowhere else I'd rather be!
You don't have to go out
Would you like to leave?
No...
"-----"
You're still the same!
"----"
"----"
Rhoslyn!
Stay silent
Would you like to come with me?
Who's there?
Uncomfortable at someone giving me honor I didn't earn
Argue
~Rhoslyn Route starts here~
What's wrong?
I just want you to be happy!
"---"
Forget I said anything
Comfort Rhoslyn
Poke it
Why?!
I want to help you!
[If you choose "Then so be it", it branches for bad ending]
"----"
....




Thank you for reading! :)