You sound very needy and she sounds very independent. You said here that you live very separate lives. Why would you expect her to be a support system when it doesn't seem like you've explicitly discussed that or grown close to each other for that to happen organically.

It is not as dangerous as you may think for young women to go solo backpacking. That's kind of closed minded thinking and diminishes a young woman's ability to empower herself with skills to do it safely.

For all you know she may have been researching this trip for a long time even though from the outside it seems she planned it quickly. If you live such separate lives you may not know how capable she is in pursuing such things.

She doesn't have to tell you everything she's planning in her life, no one does. I do think she should have mentioned it purely so you'd know she was out of town and when she would return since you are roommates. What she does when she's away is not necessarily your business and it's kind of messed up for you to judge her for what she did. It's impressive of her to solo backpack alone as a young woman.

The comments about jealousy do sound petty, but maybe there is a reason she didnt tell only you when she told plenty of others. It's not like she told no one, which would be dangerous had something happened to her.

The visiting friend situation seems like a separate issue to me, and yes, it sucks to not know if someone is visiting ahead of time. However, if you're going to be as close as you seem like you want her to be, I personally wouldn't be so upset about that. I have had many roommates, sometimes living with best friends and sometimes living with people who are merely roommates. Living with people who I'm tight with, I don't always feel so inclined to get 'permission' ahead of time for visitors. We are all friends living together in a home and we all treat it as a home together and welcome friends when they come through. So you either want this girl to be your family away from home so to speak and you don't get so bothered when she has her own friends over, or you treat her as a not so close roommate and discuss these boundaries explicitly. Can't have it both ways.