A byproduct of my Brazilian stuff - I discovered that the Portuguese Wikipedia has a list of senators for the last term of the General Assembly of the Brazilian Empire.
Now, the Imperial Senate was kind of a microcosm of the Brazilian Empire itself, in that it represented kind of an odd mix of "traditional" European limited monarchy and Enlightenment-era liberal idealism. On the face of it, its function was similar to the British House of Lords - it was supposed to be a chamber of sober reflection where the nation's most respectable men could gather and put the lid on the more radical instincts of the lower house. Whereas the Chamber of Deputies was elected directly (starting in 1881) with quite a low wage threshold for suffrage, the Senate followed an unusual mixed election-appointment system, where the richest property holders in each province chose a shortlist of candidates, from which the Emperor chose a senator to be invested for a life term. As such, the Senate was not a hereditary chamber (except insofar as adult members of the Imperial House held seats in it by right - in 1889, the sole beneficiary of this was the Princess Imperial, who was also the only female senator), but being named to it functioned sort of like a British life peerage, except that there was a limit on the number of senators from each province - they were supposed to be equal to half the number of deputies elected there, rounded down. This meant the Senate of the 1886-89 legislature had 60 seats, with Minas Gerais making up the largest number (ten) and several of the outlying provinces having only one seat. Notably, southern Brazil was substantially less represented than it would be later on, as its industrial growth wouldn't quite take hold until the 20th century.
Unlike most of the republics that followed it (the military dictatorship is the exception to this), the Empire was mostly a strict two-party system. You had the Conservative Party (Partido Conservador), which represented the wealthy landowners, staunchly supporting the monarchy, the traditional social hierarchy, the supremacy of Catholicism, and, of course, the institution of slavery. While the Conservatives mostly supported parliamentary government, they also tended to favour centralised rule from Rio de Janeiro. On the other hand, there was the Liberal Party (Partido Liberal), whose supporters were largely smallholders and urban people, and who wanted to institute reforms to turn Brazil into a proper parliamentary democracy, including the election of senators and restrictions on imperial authority. Traditionally, the main dividing line between the parties had been the question of decentralisation, which the Liberals tended to favour while the Conservatives opposed it, but after the political earthquake that was the Paraguayan War, the Liberals started to drift leftward, and starting in 1878, the Liberal government instituted a slew of reforms including direct elections to the Chamber of Deputies, public education, clampdowns on election fraud and the gradual abolition of slavery.
That Liberal government lost power in 1885, but this didn't necessarily stop the pace of reform - in 1888, while the Emperor was travelling in Europe, the Princess Imperial and her sympathisers in the Conservative government pushed through a law that immediately emancipated all slaves in Brazil. By this point, the institution was close to a natural death anyway - Brazilian slavery was incredibly nasty, with enslaved people tending to die faster than they could be replaced, and the end of the Atlantic slave trade meant that it was never going to sustain itself. Still, the traditional elites out in the provinces took this as an attack, and when it became known that the Liberals might form another government the following year, Conservative Marshal Deodoro da Fonseca staged a coup d'état to prevent this. Now, he probably didn't actually intend for it to go further than restoring the Conservatives to power, but junior officers (a constant of Brazilian army politics is that the junior officers always tend to fuck things up for their superiors) who had spent the past few years getting high on republicanism and positivism decided they were probably not going to get another chance to realise their ambitions, and so they pressured Fonseca into declaring the end of the monarchy and the birth of a Brazilian republic. That republic would end up totally dominated by a) the army and b) provincial landowners, who each made sure that democracy didn't stray too far from their ideas of good government.
I know why it was the case, but I still like that Princess Isabel got her own special seat despite also serving as Regent repeatedly (including, as you note, being instrumental in getting the Lei Áurea passed to end slavery). Ironically that almost certainly doomed the monarchy since the conservative slaveowning class was infuriated.