Is this situation bringing unwanted, unresolved feelings from the past? I think there are moments along the way when certain people or events trigger waves of unhappiness in us, even when we've been really good at being happy. I prefer to think of it like the Universe/Higher Self is showing me how to play the game better by throwing me a curveball. In other words, even if the situation seems negative, there's something there to explore about yourself, something unresolved that needs to be brought to light for healing or shifting, and with this self-knowledge - it's easier to move on and find happiness. At least that's how it worked out for me.

Did she break your heart or hurt you in the past? Her coming back like this seems like the universe is bringing you a message of some sort, maybe you have unfinished business with her? It would be beneficial maybe for you to find out why she is contacting you and then work with your feelings surrounding her. She's no longer a potential partner for you but she might be able to help you out with some things in your vibration. If you are 'flying high' then you will attract people who will help you along your journey, so she may be one. Maybe you could find out something about yourself through her that you have been blind to before but that she may be able to enlighten you with. Maybe you just need to get some sort of emotional closure from her. I would respond to her if I were you, just to see what is going on. The universe acts in strange ways, we shouldn't dismiss things that come to us like that just because we ourselves don't see how it relates to what we want. I've learnt valuable things about myself from exs years after we've broken up and got closure that I didn't know I needed years after a break up too.