Ignoring you in the hallway doesn't necessarily mean anything. I've recently discovered (thanks to a psych friend) that it's not uncommon for some people to not notice those passing by. For those of us who see anything and everyone, it's had to imagine - but apparently it's something which is true for some.
As for the amount of attention she's giving you, does she do it to everyone - or just you? If it's just you, then it's worth a try.
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.