I went through the same thing with my younger son - some kids are very strong willed and know what's best - straight from the source (Mom). He never did take a bottle nor would he ever take breastmilk except "fresh squeezed", so I wouldn't be so certain your pedi is right. She may adjust to the new schedule - but, unfortunately, that's not optimal for her health.
I was fortunate in that my son's caregiver was 5 minutes from work, so they paged me when he was hungry and I always went at lunchtime. Is it possible for your mother to bring her to your workplace at least once a day (Ideally twice) to nurse? - I had a friend who did that and it worked very well for her.
Also, I found that nighttime nursing was essential for him to get enough nursing time, as well as to maintain my milk supply. So, my recommendation would be for you to at least increase nighttime nursing (by at least two feedings) until you resolve the issue. Also, make sure you nurse frequently in the morning before you go to work - i.e., as soon as you wake up (and maybe wake up an hour early to get in an extra feeding), anytime she awakens before you leave the house and just before you leave the house. And, of course, frequent nursing once you get home is necessary.