Well two questions. 1-how on earth do I romance hildy st john? 2-how do I fly the plane accross the Atlantic?
Not 100% sure about St. John since she’s not my preferred RO, although I saw a comment that you just have to flirt with her every chance you get. I think you also have to get to Monaco with enough time remaining to have the option to contact her in person, if you went to her office and flirted with her earlier. You can continue flirting with her after you meet in Monaco.
For the transatlantic flight, you need to have a very high Drive skill (60+) and then choose to fly a plane over the Atlantic when you try to escape from NYC. As a plus, this will probably give you enough time to meet with St. John after you arrive.
I don’t think you need to go to Monaco and meet her there in order to get a romance with her. I think that it’s enough to do the following things: Firstly, do the interview with her, and while you’re there, take the opportunity to flirt with her. And near the end, just before you’re reunited with the rest of your band, you get the opportunity to talk to her again. If you take the flirt option then once more, that should be enough to get a romance with her at the end, if I remember correctly, as long as you manage to stay in your own world at the end of the game. Warning: there’s not much actually happening in that romance, so don’t expect too much.