"When I was working in France, I met my boyfriend," she said.
Reported speech - She said when she had been working in France, she met her boyfriend. Or, She said she met her boyfriend when she had been working in France.
She started working before she met her boyfriend so to show this we use past perfect continuous (had been working). We only use one past perfect in a sentence to show that one action happened or started before another action, we can't put both verbs (meet, work) into the past perfect.
When we report speech, we often move the verb one tense 'back'; e.g. was working - had been working. But it isn't always necessary. It is also correct to say, She said she met her boyfriend when she was working in France. The use of past perfect is used to emphasise that one action was before the other.