Currently weaning my daughter to formula?

she is four months old,i have been weaning since last wednesday. she had been combined feeding for awhile.now we always had this routine where when Sophia wakes up i and goes to sleep she would be put to the breast however when i gave her a bottle which was half breast milk/ half formula, she freaked and wanted the breast, we have been struggling and it is nearly a week now, she is coping better but i admit i have been letting her breastfeed atleast once a day, i am slowly cutting all of the pumping sessions down so soon she will be fully bottle fed but it is just these feeding sessions that our really hard. any ideas