Everyone has a reserve of emotional strength inside of them.
She has just recently realized she has used up most of that reserve already. She is literally letting her well run dry.
If only she had noticed sooner. Maybe she would have had time to replenish herself.
That is where her problem lies; she never thinks about replenishing herself, only others.
She would give everything up for another. She has and will continue – even though she understands the risks.
I guess that’s the thing about having a reserve, eventually it runs out.