BleBle Torchwicked If one pays money to an artist for sprites/tiles without looping in SL, there's a chance she won't like the result and stick with the current assets. If someone really wants better, the best bet would be to go hunt for better free resources and show them to SL.
If no free resources of good quality can be found, then for one month, join at the $50 tier for Patreon and ask SL to use the money specifically to commission nicer sprites/tiles for this purpose. Maybe talk to her first, about what you're trying to do and what exactly you want to see improved about those graphics, if you want to be sure you aren't risking your money. (Per the $50 tier description, "If you want to specify that your donation be used for something specific (art, scripts, etc), talk to me and I'll use it to improve the game in that way. ^-^")
The second suggestion does assume the "WTB" in the thread title isn't wholly joking, of course.