In chapter 4 of Rut, after Boaz performs yibum with Rut and she bears a son, it says:
וַתִּקְרֶאנָה לוֹ הַשְּׁכֵנוֹת שֵׁם לֵאמֹר, יֻלַּד-בֵּן לְנָעֳמִי; וַתִּקְרֶאנָה שְׁמוֹ עוֹבֵד, הוּא אֲבִי-יִשַׁי אֲבִי דָוִד.
And the women her neighbours gave it a name, saying: 'There is a son born to Naomi'; and they called his name Obed; he is the father of Jesse, the father of David.
The yibum was clearly performed on behalf of Machlon, not Elimelech, per verse 10. So this isn't some sort of proxy arrangement on behalf of Elimelech (who anyway had produced sons).
So what does it mean when it says a son is born to Naomi? Does this just mean a descendant (since her other sons died), or does she somehow have maternal status (which may be related to her nursing the child)? If she has special status, why?