Many of us are saying your behaviour is the red flag, OP. You've woven a story from a few details and lots of your own assumptions and prejudices, and are using it to justify intruding, manipulating, controlling the life of another adult.
You may be right about this person, your daughter may have terrible boundaries, groomed by you, and have a difficult learning experience ahead.
Or she may have great boundaries, from a lifetime of fending you off, and sail through.
Or there may be nothing more than friendship here, or colleagues networking. Social mores have changed a lot and you are not the morality police.
Or this may be the love of her life, about to get divorced, the father of your future grandchildren. Be nice!
Or perhaps her great love has already swung by, taken one look at a lifetime of over involved in-laws, and run for the hills. Oops.
Seriously, OP. Your own behaviour is bonkers.