Maybe ship, maybe platonic but once Luisa is able to open up about feeling overworked, Isabella likes to take her out for fun nights on the town so they could just relax and hang out, maybe get spa treatments and manicures (anachronism or modern AU? idk but manicures is like THE ultimate girl bonding activity according to TV so lmao). They could just cut loose and Luisa doesn't have always be working and Isa doesn't have to always be perfect. Sometimes they'll bring along Mirabel or Dolores too (and at least once Camillo on accident while was posing as one of them), but mostly it's just the two of them.
Someone might still ask a favor of Luisa and she'll start to do it because she's so used to it but then Isa will go "ACTUALLY this is her day off, I think you can manage it by yourself :) ".
Yes! Luisa deserves all the spa days she wants! If you don't want a Modern AU, maybe there is a naturally occurring hot spring within or nearby the Encanto that they can go to. Oh! Or like in the concept art, they could go to Isabela's garden. Regardless, yes, Isabela would definitely make Luisa take days off and treat her to something nice.
What works so well about Luisa and Isabela (ship or not) is that Isabela would absolutely help Luisa maintain healthy work/life boundaries. As the older sister, Isabela is probably especially protective over Luisa and wants to make sure she takes care of herself.