Personally I'd be upping her milk or trying hungrier baby milk, early weaning should be done as a last resort.
At around 4 months babies do go through growth spurts which a lot of mums think is a sign for weaning, when in fact it may pass after a few days.
DD I gave some food at 20 weeks but wasn't happy with my decision, so I then held her off and went mainly down the BLW route. DS was exclusively breastfed and always hungry, feeding 2-3 hourly day and night, sometimes feeding up to 6 times overnight. I tried him with food after considering the possible health risks at 18 weeks. He took it the first time I tried but from then onwards he refused so I offered him some every week or two to see how he got on. He really wasn't ready for it until he was 6 months, so although hunger wise he could have done with it, physically there was no way he wanted it.