Excercising is important and it's not just for getting stronger or burning fat, there are more complex activities happening in our bodies.
Yeah, I was thinking… I don’t think she produce hormones anymore. >_>
She appears to have some form of blood circulation with the blushing (without heartbeat?) and still eats food so we can assume other functions like hormone production are also working. Another factor to consider is her showing feelings and various levels of stress which are influenced by hormones.
I think there are more examples like with sweating.
If she has hormones then you know what else might be possible?
According to all the info so far, it looks like a lot of her body got damaged in that accident and she might've lost functionality of some vital organs like the heart but the talisman and other stuff are keeping her alive.
Also she could be healing bit by bit.
For now her biggest problems are stiff joints, not being able to move much or express herself more which is slowly getting better.
Not really "undead" as I know it. More like someone who is on life support while recovering from injuries but can also move around.
Of course these are theories I made using the clues we were shown so far.
I am also very much in favour of a happy ending where she gets better or they get together anyway. Hence there is a bit of bias from me. ¯\
(ツ)/¯
Personally, I wouldn't mind if the solution to her "undead" problem turns out to be love, exercise, time, etc. because this isn't a very serious manga (at least for now) and it's possible that won't be resolved and even if it does it might be a bit too sudden or unsatisfactory for some.
It is entirely possible for the author to write off these 'clues' as something merely done for aesthetics or relatability and take it in a very different direction such as one where she will slowly fall apart or one where she has to watch him die of old age and then... y'know?

But that probably won't happen because there is an intended audience. I
might be am overthinking.
I don't think scientific accuracy and really serious stuff are on the menu but that ain't stopping us from theorising.
