Laine's implication is simple: either you find a true love, or you find someone who can help your career.
As for Claudia, Laine believes that she is not Afu's true love, just a momentary impulse.
In fact, as Laine said, it's not impossible for a female servant to successfully marry into a great noble family, but successful examples are very rare. Most of the time, they are played by the great nobles until they are discarded like damaged goods and can't even become female courtiers.
It's not so easy to pick something ready-made. Strictly speaking, Laine was chosen by the Surya family, which counts as a political marriage. However, they have accumulated quite a bit of affection along the way, making it a rather decent union.
And generally, the wives of great nobles and generals fall into two categories. The first is a true love who followed him when he was a soldier or hadn't fully risen to power; the other is someone who can help his career in a political marriage.
