was in touch with an SB over the course of a year. She lives a few thousand miles away from me, so I tried to hook up with her whenever I was in her neck of the woods.  She was a firecracker, and a bit of a mess at times, so actual meetings were always hit or miss, although last time she refused to let me give her an allowance for the meet, saying we were friends by then.  

Well fast forward 6-8 month since the last time I saw her and probably 4 months since she answered a text.  Recent text indicate her number is no longer her number, and she has not looked at her SA profile in well over a year.  I can find her on instagram, (she sent me pictures in the past with her instagram account name) and she seems to be doing well and has a relationship as well.  

Should I reach out via instagram as I am going to be near her again, or just drop it?  

If she was changing her life — as you’ve already gathered — and if she can’t be reached the way you previously did, then you’ve answered your own question: she’s moved on.  Which is painful—it happened to me recently and this one moved to within a few miles of me when she dumped me after 2.5 years. I don’t how it’s anything other than a choice to move on for her, and you are left with the consequences.  Sorry to be a downer.

If she just went silent you can probably ping her (as opposed to an explicit "don't contact me any more!"  But silence is an answer.  Accept it.

If it seems she is in a relationship, then do not contact her.  As others said, sounds like she is trying to turn it around.  Just like dating a SO, when they move on, it is time for you to move on.