I think that parents are best suited for support and picking up the pieces once they fall.
Excellent advice! Anything more is triangulating, which gets incredibly messy!
I know this is a very tough issue, and I have lived it a number of times with my uBPDd who's now 26. But remember, the suitor might not believe you anyway, and this could cause your daughter to split you and paint you black (and yes, I've experienced both.) Just be supportive and let them figure it out.
Best,
PictureLady