I would not assist feed her. If she's almost 1000 grams she knows how to eat; this is not a baby that needs a jumpstart.
If she's 900-ish grams at four years old she likely never was a good feeder. I have/had one like this, every few months she would eat once or twice in a row, then she'd stop eating again. Averaged out she was only eating every 5-6 weeks. She's healthy enough, just small.