Did you ask her why she removed the ring?
All I can say is that out of everything put together it sounds like she still has feeling for him. However, this is not necessarily a bad thing because love is not something you turn off and on like a light bulb. If she's never lied to you before, or given you reason to think she has lied, then I would try to let it go and take her word for it. It's not going to do any good to dwell on it. We can never know what's truly in someones heart, and that is the risk of love, to take them at their word. Perhaps what you saw is what she needed to do to get through those last moments with him and close that chapter of her life forever.
I welcome your thoughts, let me know if you want to talk more.
Why don't you go with her? how does she know he's not going to be there? how did he wind up with a house in the same complex as her parents?
You love this woman enough to ask her to marry you, so now you've got to trust her. If you didn't trust her, then you should not have gotten engaged in the first place. Don't be nervous, give her your support, trust and faith....there's always a chance that she will betray you, but that can happen with anyone, at any time. If you let it drive you crazy, you won't even trust her to leave the house. Unless she has given you reason to think that she would do something against you, then you have to let it go and trust her.
I'm here if you want to talk more