Hi,
1. The girl that I'm meeting tonight had two boyfriends. This means that she doesn't have them at the time you are saying this. She had them at a previous time.
A week later, I tell my friend:
2. The girl that I met last week had two boyfriends. This sounds like she had them at the time I met her last week.
3. The girl that I met last week had had two boyfriends. This makes clear the situation as outlined in No. 1 above. Therefore, to be accurate, this is what you should say. It's quite a normal, everyday kind of thing to say. Of course, you may not care about such accuracy, that's up to you.
Do I need to use reported speech here? It's not speech that is being reported, it's just describing a situation in the past.
Best wishes, Clive