I think the most likely reason for her B12 shots and abd surgery is a history of
crohn’s disease which makes you susceptible to low levels due to inability to absorb some foods, or a diet low in such vitamins Crohn’s can lead to a depression and isolation esp in younger people. The pain, nausea, bloating etc associated with it as well as other chronic conditions takes a toll on people. It could lead to having pernicious anemia as a result of low absorption and lack of a healthy diet. Which we see her in many past videos eating high fat, sugar and a low fibre diet. B12 is sometimes given for an acute depression. I know many that have had this. They may not eat well during their acute situation and therefore need this supplemental injection. I think instead of trying to be open about her condition in early years, she tried hard to hide things and overly focus on her appearance and shallow things. this can lead to eating disorder in young kids, especially girls. I once worked with young people needing hospitalization for eating disorders and commonly they were very manipulative and lied a lot. They needed supervision to eat and afterwards to make sure they didn’t vomit. Frequent episodes of vomiting leads to ulcerative diseases in the .GI tract and they are more at risk for cancer etc. It was very very difficult to get them to agree to get help. Their parents had to basically admit them involuntarily. If you pair that with a chronic illness, stress at home due to her parental relationships etc you can see how this type of personality develops.
All this is speculative of course but it does seem to fit in with what we see in earlier and current vlogs. There are many combinations of the above that may be at play. We likely will never know though.
Because as an adult she seems to avoid things for long periods of time. Her mother cant force her to have regular monitoring and she likely isnt open about her symptoms either. Probably avoids going to doctors for preventative care. She lived in a dorm at uni so easier to hide things from your family. She isn't one to listen to others either as we clearly see. She ignores and blocks wise advice etc.