The choice is not merely stylistic.
The general rule is that suus refers to the subject of the clause, eius to someone else.
There is some variation between the two, but the general rule of thumb is that there is a difference.
Your first example can be simplified to: Mater maritum suum/eius expectat.
With suus the mother is waiting for her own husband.
With eius she is waiting for someone else's husband.
In isolation it feels weird, but with some context we can make the contrast:
Mater cum amico in horto sedens maritum suum/eius expectat.
Sitting in the garden with her friend, the mother waits for her/his husband.
I chose the friend to be male so that I can make the English contrast in one word.
If you use amica instead, it would be "her own husband"/"her friend's husband".
In a subordinate clause suus can also refer to the subject of the governing clause, so there can be ambiguity.
Marcus dixit Gaium se amare.
Marcus said that Gaius loves him/himself.
With "him" se refers to the subject Marcus of the governing clause, with himself it refers to the subject Gaius of the subordinate ACI structure.
Both are valid readings.
In your second example eius looks like the only plausible choice, unless you argue that there is effectively subordination that makes reference to the girl possible.
You can say Caesar in castris suis manet when Caesar stays in his camp, but what does it mean if tears are in their own eyes?
As tears have no eyes, one would interpret in oculis suis as in oculis eius.