I agree with NyIndech- it's not really anyone's business is it? Apart from their own, and God's.
We know that we're all sinners, and that at least some of the congregation at our churches go to Confession (hopefully, us too!), so the fact that we all sin should be no surprise to each other. IF the lady in question is expecting out of wedlock (and you should always assume the best- for example, when my Mum was expecting after several years of marriage, her fingers swelled up so she couldn't wear her wedding ring. I'm sure there were probably a few raised eyebrows from nosy Catholics!) then it's wonderful that she is coming to Mass instead of having drifted away or lost the Faith, as so many do.
If we all had our sins paraded around, we'd be mortified. Young unmarried girls who find themselves expecting have to bear the consequences for many months and years, even if their sins are confessed and forgiven long ago. To come to Mass when they know others may be giving them the eye and looking at their ring finger takes courage.