lol
Sure!
I pick up the phone, dial her number
Ring…Ring
Her dad answers it, not her, because they recognize my phone number
“Hello,” He says.
“Hi, can I talk to (her name here)?” I ask him.
“Uh, I don’t really think that’s a good idea.”
“Why Not?”
“Well, we have our rules.”
“What’s wrong with talking with her on the phone?”
“Well, I believe that you both deserve God’s best, and talking together like that may not be that.”
“Why not?” I ask, yet again.
“Well, we have prayed about it, and we have decided that she isn’t ready to do that just yet.”
“We?”
“I had a talk with her, and we agree that she isn’t ready for that. I have no ulterior motive here, she really agrees.”
~Now, let’s interrupt this for a second. This is actually based on a conversation I’ve had with him. Including the “God’s best” phrase, as well as the “We prayed about it, and we talked about it…” “I have no ulterior motive” etc.
I have a hard time believing that last part. Both from what I’ve heard from people who have experience in this matter, and from the actions of the young woman as well.
Let’s get a little bit more radical in this “conversation”:
“Well, I really have a hard time believing that, sir.”
“Why’s that?”
“Because it seems to me that she likes me more than you’re allowing her to.”
“Well, I wouldn’t say that. After all, she’s given me charge of these affairs.”
OK, if that’s really how the conversation would go - that is REALLY creepy. I have to take your word for it that she is not being abused, but all of this would send up a BIG red flag. Maybe other daughters have different relationships with their Dads, but IMHO this is really creepy.
OTOH, what you need is some subterfuge. You need to borrow a cell phone of a mutual friend or go to their house where you can have them make the initial phone call so that you can get past the ‘guard’, so to speak.

Or have the friend set up a meeting somewhere, i.e. library, park etc. - whatever she does with her girlfriends. (I can’t believe I’m actually suggesting this for a grown woman.)
Or the letter might work, but how long will it take you to write it, mail it etc.? Does she have e-mail?