All her references to putting herself first now, shining bright, upwards and onwards blablabla suggest to me 1. Her having to 'compromise' to move to India, 2. Her having to 'compromise' to move into the shared flat. 3. Her 'compromising' her future with uncertainity about Joe's job. 4. Her 'compromising' to accommodate his full time job.
I really think that he wanted to move into the shared flat knowing he would move back to India or Dubai again for the job sometime soon. She was probably already pissed but not expecting the job move and then when he's decided he's going there no matter what, she's snapped. Maybe he also wanted to delay the wedding because he wasn't sure what the future looked like?
I mean I get if she knew that for 2 years they'd live abroad but if he wants to do it indefinitely, doesn't want to settle in the UK and possibly didn't want to get married if she didn't want to live abroad indefinitely, it can all fall apart very fast. Maybe she imagined wedding, buying a 'forever home', starting a family but he sees another 5 years abroad at least, if not more, with no plans to settle anywhere.
For example. three of my ex classmates from high school, three women - each were in a very long term relationship, one bought a house with her partner and shortly after got engaged and within six months, suddenly single. Second one, bought a house with her partner, not soon after, moved to France to teach snowboarding and obviously the relationship is over. Third even had her bachelorette after living together, engagement, constant gushy instagram posts about her man. Even posted '15 days to Mr. and Mrs. ____' and then suddenly, single as well.
I think big life decisions and some built up resentment can quickly cause everything to implode. Doesn't necessarily have to be cheating level 'bad behaviour'. You pretend everything is okay (from both sides) and then one thing pushes you over the edge.
Edit: Her references to a 'shitstorm' also makes me think that plans changed very fast and unexpectedly that ended up at a point where he couldn't offer her anything she wanted and she was pissed off by all the changes. i.e him possibly jumping to a new job in India/Dubai without even considering what their future would look like.