I don't think you should expect her to be served champagne or any drink at all. Also do not expect a refill even if they do offer one drink. I think one is enough and it's really time for her to go back. In fact ideally, really, you should go back and have a chat if people are awake there. In any case it's just not right to allow a situation where the passenger not seated in F may be remotely deemed to be lingering. It's bad enough in Y or any other cabin to cause any nuisance by talking etc especially when not seated there, let alone in F.

Timing-wise, you need to ask the cabin crew. It's not really up to you to choose.

Do not be offended if cabin crew says no, though. There are other F passengers to consider who are their primary concerns.