I would venture a guess that this dream uncovers your own hidden fear that your son migh marry an ugly girl. That fear was probably pushed deep into subconsciousness and now it surfaced. It doesn't matter the your daughter in law is not ugly - what matters is that it was your fear that maybe she's not all that good looking, that maybe you didn't do a good job judging her looks.
There are probably other important details that would help understand this dream - like what does that room or space remind you of, maybe some situation where you were afraid of the impression you will leave on others; also it's important how you felt about the other people at the table (were you concerned about what they would think and so on).
In general, I'd say the dream uncoveres your own vanity and some type of selfishness as well as unnecessary fear connected to your son and daughter in law.
Other possibility, which I have doubts about, is that maybe somewhere below the surface she really is "ugly". For this, I'd expect some type of "revealing" to take place, rather then just observation of her looks...
Obviosly, if my first interpretation is correct, there would be a few things to learn for the dream: you tend to judge maybe too much; that judging brings unnecessary stress and anxiety.