This feeling in initial days of married life is not very uncommon. Knowing a person from across the table for a two hour date is very different from spending 24/7 with them. And one only realises this after marriage. Adjustment, empathy and compromise from both the partners are very important pillars to make a marriage work, and this is exactly what you need to make your daughter understand. If there are no serious and big issues (that cant be sorted out) then you need to explain to her, that if she is not happy with a man after 3 years of courting and knowing each other, how does she think she'll be happy with this colleague of hers.

These kind of inclinations happen because if a third person is aware of the distances between a couple they can easily and happily make use of this opportunity by lending a shoulder to an already vulnerable individual. Your daughter needs to understand that such a childish approach is only going to worsen things. If things still don't get better, you could take them to a neutral party for counseling.
All the best!