S.H.
My empathy for you and your situation.
At this age, you cannot feed her according to a "schedule"...a baby needs to be fed "on demand" whether by you or the babysitter. No wonder she is frustrated and hungry... this is not good. You need to provide the sitter with more breastmilk than you think. BECAUSE, as a baby is growing and changing, their intake needs changes too. They will need more, and like any human or adult, their appetites WILL fluctuate everyday too. It's normal. You cannot predict this.
THUS, you need to provide more than what you think.
I had this problem when I was babysitting a baby once... the Mother insisted her baby didn't drink that much, and would only provide 2, 3 ounce bottles for the WHOLE day! It was very frustrating... for the baby and me. I eventually stopped babysitting the child.
A baby needs to be fed whenever they are hungry... and sometimes they will even need to feed every hour.... you have to look out for their "hunger" signals as well.... not just according to a clock. This is for bottle, formula OR direct breastfeeding.
For the first year of life, the PRIMARY source of nutrition for a baby is breastmilk/formula. NOT solids. NOT water.
Solids at this age is supplemental...for them to get used to "eating." It is NOT their primary "meal." Solids, whether in quantity or frequency, is GRADUAL. Starting from one "meal" a day...then over time (even a month), 2 meals a day... then 3 meals a day. There is no rush to this. And you should not "make" a baby eat 3 meals a day from day one. They and their body had to adjust to it... your babysitter should know this. "Serving size" at this age is just in tablespoons, not jars. Remember their stomachs are tiny. They get full fast.
ASK your Pediatrician for guidelines and what you should use as a "first food" and then how to progress form there. Each Pediatrician has different "styles", some being more conservative or liberal than others.
When you breastfeed, you need to make SURE you nurse her long enough so she can get to the "hind" milk... this takes at least 15 minutes or nursing...then you should continue to let her nurse some more, until she wants to stop. Also making sure she is latching on correctly to get the proper nursing intake.
You should ALWAYS give breastmilk FIRST...before solids. Or, they will be too full to nurse or drink their breastmilk. AND, if you "replace" nursings with solids... this will affect your body's production of breastmilk, reducing it.
Ask your Pediatrician for how much breastmilk she should be drinking at this age as well. If you cannot produce enough pumped breastmilk to fill enough bottles for her, then you need to assess how you will supplement her? Formula? And how will you feel about this? Ask your Pediatrician. Because she will need to have enough on hand, at the babysitter. You don't want to "run out" of bottles for her while at the babysitter.
Sample:
baby wakes up
Nurse her for as long as it takes
take her to babysitter
Have babysitter give her bottle
Midmorning- try a little "solids." (per recommendation from your Pediatrician).
bottle before nap
bottle after nap
bottle whenever your baby needs it and is hungry, on demand
"lunch time" -solids. IF she is on solids, following breastmilk
bottle before afternoon nap
bottle after afternoon nap
bottle before "dinner" if she is on solids
Bottle before bed
Direct nursing during the night-time when she wakes up and is hungry.
At least this is what I did for both my children. I prioritized breastfeeding as my main thing for the entire first year... then, fed my kids "solids" after breastfeeding. My kids grew like weeds.
Each Mom is different... refer to your Pediatrician. Make SURE your baby is getting enough intake... she does not seem to be right now.
All the best,
Susan