Every wake that I've been to is before the funeral, and it's held at a funeral home or other professionally arranged viewing place. And so there is already an expectation that there will be flowers, and the funeral director has all the arrangements for that in place--far more so than with a wedding, in fact. Anything taking place *after* the funeral service is a gathering or a memorial service.
At my mom's funeral, we called that "the family visitation" or "the visitation" instead of "wake."
In those instances I think you can bring an arrangement of flowers to the wake, and simply hand it to the funeral director who is running the wake (if that's where it's held). Then the staff will figure out where to put it. It might be a nice gesture that will be noticed by the family. I know that I saw the flowers sent by a friend of mine, and it really, really touched me to see them there.
But I don't think it's necessary, and I think a FAR more valuable "gift" would be for your DD to sit down and write a longer letter of condolence to the widower and to Tina's parent, and to Tina--three letters. And to tell them of a memory of spending time with Grandma, and saying, "I too will miss her, and I wish you comfort."
And other phrases based on the specific beliefs of those involved.