What a woman may not ask for
The reason given closes the whole question.
لاَ يَحِلُّ لاِمْرَأَةٍ تَسْأَلُ طَلاَقَ أُخْتِهَا لِتَسْتَفْرِغَ صَحْفَتَهَا، فَإِنَّمَا لَهَا مَا قُدِّرَ لَهَا
Lā yaḥillu li-mraʾatin tasʾala ṭalāqa ukhtihā li-tastafrigha ṣaḥfatahā, fa-innamā lahā mā quddira lahā
It is not lawful for a woman to ask for her sister's divorce in order to empty her bowl into her own. She will only have what was decreed for her.
Where this comes from
The image is of tipping someone else's plate into yours. The reason it is pointless is given straight after: the amount was already set, and moving it from another plate does not change it.
The full narration
Narrated Abu Huraira:The Prophet (ﷺ) said, "It is not lawful for a woman (at the time of wedding) to ask for the divorce of her sister (i.e. the other wife of her would-be husband) in order to have everything for herself, for she will take only what has been written for her
Source
Ṣaḥīḥ al-Bukhārī · 5152
- Agreed upon as authentic (al-Bukhārī / Muslim)