Mexico, just as USA, has three branches in government. Two of them are elected by popular vote (President and Congress) and the other one by internal vote (Supreme Court).

In the past, Lopez Obrador tried to change Constitution via reforms on various subjects. A couple of them were so controversial that divided the Congress in two: those of his party vs. those of other parties. The latter won just for a bit for the super-majority requirement for that type of reform.

Aside from that, the Supreme Court also didn't support some of those reforms. So, just as any authoritarian figure would do against their opposition, Lopez Obrador intended to change how the Supreme Court elects its magisters and judges, turning it into another popular vote branch (which he could control just as with Congress).

Back to the present, Sheinbaum will have that super-majority in Congress that Lopez Obrador didn't. That could allow her even reforms to the Supreme Court, effectively disappearing any opposition to whatever reform they wanted to pass.

So... let's just hope she has good intentions.