But that could equally be other things: carrying a minor injury/missing some training; her (ridiculous) over distance training was such that she simply lost her speed; she was competing during a heavy training cycle.
To assume it's simply that she 'wasn't trying hard enough' is the least likely answer, IMO.
And let's be specific where we can: she doesn't have a '1:54 PR'. She has a 1:54.97 PR, which is basically 1:55 flat. Why do I say this? Not to be pedantic, but because, for example, Ana Quirot ran a 1:54.4 PB in 1989, then for the next two seasons she was running 3 seconds slower at 1:57.4, and she wasn't injured. Sigrun Wodars had a 1:55.26 PB, also from 89, and ran 1:55.87 in 1990, only to drop to 2:00.59 the next season (nearly 5 seconds difference) when carrying a minor injury. Kratochvilova dropped 4.4 seconds between 83 & 84, not injured. I use those examples as I mentioned them earlier, but look at someone like Jemma Reekie who dropped 3 seconds between last season and this.
Mu has dropped 5 seconds over two seasons. The big drop was 4 seconds between '23 & '24. She ran just two meets in '24, and nothing before the US Trials. Was she injured? Was Kersee restricting her racing schedule (he let SML race)? Clearly there was the possibility she could have run faster than her 1:58.84 SF & Qualified for Paris had she stayed on her feet in the final.
I think, psychologically, that fall had a huge impact on her, mentally. Then Kersee had this wild idea of making her run intentionally slowly paced 1500s & a 5k, and, well, she's done. But even so, she still ran 1:59.7 which I actually think is impressive after opening with a 2:03.4 a month earlier.
There's no doubt the ability is there. But if she isn't motivated, it's no wonder after she's been given such a ridiculous training & racing schedule. If she can switch coaches, get back to 400s & 800s, I've no doubt she can get back to 1:55+