Just have a nice heartfelt talk with her, before she moves out.
Not a talk about making her feel guilty or about judging her or teaching her a lesson or "lecturing" her... just a nice chat, heart to heart, about how proud you are of her and how she is growing up and how you realize that... and how, when you were her age you were a Mom already... and you will always be her Mom and she will always be your daughter no matter what age, and you are ALWAYS there for her.
Don't tell her about all the "regrets" you have or had or how you wish you did things differently. How you did thing are how you did it at the time... trying your best at the time. TELL her you love her and hug her... NOW.
Don't think about the past or how you should have... hugged her more. Just do it, NOW.
Ask her her own thoughts. Discuss things and chat.
That is what a daughter needs... a Mom that they can talk WITH... and feel open WITH... and rely on... no matter what comes up.
Because, a daughter will shy away from a Mom, that only makes her feel guilty or makes her feel inadequate. They need a parent who believes, in them... and will guide them. No matter what age.
Don't just think about yourself... but about her. Now. How she is now and what she needs, now.
She is not a "little girl" anymore. But a child, no matter what age, will always be your "child." And a child will always need... their parent.
Give your "child" wings to fly with.
And hopefully she has a JOB.
And a savings account and a checking account at the very least.
If not, she cannot support herself and rent.
I assume, she KNOWS how to look for an apartment?
And has her own medical insurance????