Cali, It's okay. Sometimes we have to answer them honestly and that's what you did. She asked you if you were happy and you stated exactly how you felt.
As for her changing the way she's feeling right now...that's what it is for now...she's venting because that is how she feels today. Tomorrow, she may come up w/something else to be unhappy about..but it's not your circus, therefore it's not your parade to worry about. She's going to find something to complain about even if a teeny ant crosses her path when she's searching for that illusive happiness.
So you had a backslide...that's okay. It's one step forward, two steps back. She now knows exactly how you feel and she's going to need some time to digest this information. Give her plenty of time and space to choke on because she truly needs it.
The dust will settle and you'll have plenty of time to interact w/her again. Don't beat yourself up over this...it's something that had to be said and now you need to get back up on that horse called detachment and continue moving forward.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.