Jane Foster absolutely deserves to be worthy to wield Mjolnir in the Marvel Cinematic Universe. The Mighty Thor comic book series is great, and in the source material, Jane is worthy of wielding the hammer. The only issue is that with the way Thor: Love and Thunder gets written, she isn't actually worthy, and that speaks to a larger problem with the film.
In a series of flashbacks exploring Thor and Jane's relationship in the MCU, it comes to light that Thor essentially casts a spell on Mjolnir, promising that it will always protect Jane. That is the explanation given for why Mjolnir calls out to Jane and ultimately why she gets the power of Thor. It has nothing to do with whether she is worthy, and that sucks.
In the comics, Jane is worthy to wield the power of Thor because she chooses to. And despite the fact that using Mjolnir accelerates the cancer in her body, she will continue to use it because it is the right thing to do. In truth, Jane is worthy to wield Mjolnir because she is a good person -- it's simple, and there doesn't need to be anything more to it.
That is where Thor: Love and Thunder unintentionally undermines Jane's role and her agency. The film tries to have the same subplot that using Mjolnir accelerates the cancer and is slowly killing Jane. But now that the basis for her getting the powers of Thor is different, it shifts the whole thing off base.
Whereas in the comics, Jane chooses to make the sacrifice herself, in the film, Mjolnir's promise given by Thor to protect Jane is instead killing her. And Thor: Love and Thunder tries to have its cake and eat it too by having a moment in the finale where she chooses to wield Mjolnir one more time even though she knows it will likely kill her. But it ends up being rushed, and before the audience can process it, she dies to support Thor’s story.
Yes, it is Thor's franchise, but Jane deserved better. Thor: Love and Thunder is fine in a bubble, and Jane is given far more agency as a character than she got afforded in films like Thor: The Dark World. However, the film's adaptation of Jane's journey as the Mighty Thor shows a misunderstanding of what made the original text work so well. Fortunately, with the post-credits scene, it seems unlikely that this is the last audiences will see of Jane or the Mighty Thor in the MCU.
To see how Jane's journey gets mishandled, Thor: Love and Thunder hits Disney+ Sep. 8.