I’m thinking about mailing flowers and perhaps some tasty snacks— anonymously of course.
This friend is often uncomfortable with romantic situations, particularly ones where reciprocity is of question. So I hope to do something to just make her feel loved and happy for a moment without inducing a goulish nightmare.
Another note is that I live in another city and have a busy schedule, so making any kind of personal appearence is not a possibility.
They live alone.
As for decoration, I’d say mostly casual with the exception that the flowers would clearly signify the Valentine’s Day-ness of it.
I asked them what they would recommend as a gift to a very special someone on valentine's day, then sent them that gift. They were "actually very surprised".