It will reapear when you're having a pleasant conversation with the sim you want to turn. I tried it many times.
My tent-dwelling Sim (her tent is placed on a 4 tile square so it'll count as a micro home) had Vlad come visit, as he does. Because she has no door to lock to keep him out, I decided we would befriend him instead. She now has a 100% friendship bar with Vlad (micro home relationship gains FTW).
"Ask to Turn" comes up CONSTANTLY as a suggested interaction, and he's also called her and asked her to come to his house to offer to turn her into a vampire. She also threw a dinner party at his house, which is where I learned that poor Vlad has Withered Stomach (ouch, I'm so sorry!).
(They're the weirdest friends ever, btw. For the longest time the only trait she knew was "music lover" and she had the adoring sentiment towards him. LOL! I haven't turned her because I've built her life around her "loves the outdoors" trait.)
OTOH, context makes a big difference. Vamps won't train, turn, spar, or any of that unless they're in a good mood, the context is pleasant, and they have a good relationship with the other Sim. Vlad in particular is a loner so if he doesn't know your Sim very well he gets tense around them and won't want to turn them. Also, if he randomly shows up during the day on the lot with just a tent that option isn't there and we rush him home and hang out there (because BURNING IN THE SUN VERY UNCOMFORTABLE Vlad is also extra-flammable).
I also don't know if there's an age difference involved in your case; my teen vamp who'd previously sparred with her dad had those interactions locked out recently.
[edit] And now, in a different save, my Sim couldn't propose marriage to Caleb and then ask him to turn in the next breath. I'll try to be patient. Perhaps it's the wrong context. I so lie, it was right there under friendly, never mind!
