"We had a very loving relationship at least until one year ago, however she now seems to be a different person."

Thinking outside of the box

1. If not at present, in a month or two she won't be any different to her friends and relatives. She will always be different to you and you will always be different to her.
2, She might also think you are acting differently towards her friends and relatives and you might think she is acting differently towards yours. 
3. Everyone in here has had an extremely loving relationship turn sour on them..
4. Everyone in here can say their loved one is hurting the one they love the most. 
5. Everyone in here has a partner in waiting and sometimes they wait without ever making contact again.

All of the above can be related to the UNITED FRONT you shared when dealing with others. It has to be they are waiting for this united front to appear out of the past, or into the future. It has to be it has disappeared out of the present.