Don't think you're wrong to feel hurt, but I also don't think your friend has done anything wrong?
People come and go and have different priorities according to life reasons.
Six weeks is nothing if you're not working together or have a physical reason to be in the same location.
I wonder whether due to your trauma from your relationship with your sister, you aspire to a level of closeness and long term connection that really isn't feasible in adult friendships?
Like you're looking for a new sister replacement or that 1-1 connection.
But really, most people don't have that emotional bandwidth apart from with partner or children.
I used to feel quite hurt and rejected (like you) when I felt there wasn't that longevity in friendships...but really it's quite common for either party to have reasons to move on or rejig their life and priorities? The only constant in life is change.
I've also had connections where the other party seems to get a bit too clingy and intense unfortunately...
For example, I've had ex-friends getting upset because I moved city.
Especially as I'm the "nice" friend and I am supportive and do things for people.
It felt like they wanted me there FOR them rather than for me.
Years on ..glad I ignored them. People come and go.
(absolutely NO reason for me to stay in a high Cost of Living area with bad memories, but they liked me "there for them".
It felt very selfish, especially as they had decent accommodation with significant family financial help which I didn't!).
It felt like they didn't want me to be thriving and moving on and were clearly showing it...
"Sometimes I feel like I don't even know her anymore. There's a wall up that never used to be there. Because there are so many things going on in her life now which she doesn't involve me in that I can't keep up."
It sounds like you're not happy with her for changing? Why shouldn't she change?
People have needs and problems and lives that extend beyond your connection with them, or your needs.
Maybe she's had some unhappiness/practical issues /financial concerns/wants to change career and needs to build up her networks for that.
Expecting to be automatically included in her new networks is a bit too much!
If you're more content and want to stay the same (nothing at all wrong with that, great you've achieved it !) then you will have less in common.
That doesn't mean you're wrong, just different people moving in different directions.
I'm sorry for all your family losses, and agree with pps...other friends, or develop ways of self-care and self-soothing? The only person you can rely on is yourself.
Step back from this friend without making a big deal about it.
I'd be appreciative of the support she's given you without expecting that level of support to be constantly available.