I think a narrow meaning of "ehrlich" for joli seems very unlikely, not least given the way SD uses it: a letter that toddler Wilhelmine writes is joli, she says that two-year-old Fritz wants to learn to exercise so FW will find him joli, a little chariot is joli and little baby Friederike is getting more jolie every day, which are two of those instances where it seems to be used in today's sense of "hübsch" - but then you also get a sentence like Wilhelmine a été fort jolie et a demande pardon a son frere (after she was punished for scratching him) a couple weeks later, which is once again a description of behaviour. Or this one: Wilhelmine se prepare pour vous montrer a votre retour ce qu'elle sait de I'histoire, et Fritz dit qu'il vous aime et qu'il veut toujours etre joli pour vous plaire.
So it seems to be a rather broad descriptor of desirable and "pretty" traits, and maybe Heinrich used the German word that seemed closest to what he specifically meant in his particular case? And one thing I had to think of: the philosophical tradition of "schön" = "gut", which could play into a broader meaning of joli as a descriptor?