FionaHi C
I don’t have children but I would suggest that you try and continue for at least another 3 months till she is about 6 months then start her on formula - this is what a number of mothers do in Australia. Up to 6 months they still need the nutrients in Mum’s milk. If you do need to pump it into a bottle then why not mix the salt with it at the same time.
Fiona