Your emotions can be human or can be like football. If you let her play with your emotional balance then it was completely by your own choice. There is nothing wrong in talking to her or responding to her. But you don’t have to necessarily know why, what of her actions. The best way you can answer her is by being polite and never asking about your past. If you respected the relationship then find out if she is happy being there. Give her benefit of doubt she might have lied you because she didn’t have enough strength to tell the truth. But if she is happy being there then there is no reason for you to be unhappy . This is the best thing you can do to make her realize that she too lost a good relationship. At the end of it, these are trivial things in the bigger picture of your life. Couple of years down the line you’ll be sitting with a cup of tea in your hand and smiling at yourself for this emotional disturbance you are going through.

All the best my friend.
Harsh