Need advice

Chelsea
So my daughter was born at 33 weeks and she was immediately taken to the NICU. I had to pump to get my milk started and now she is home and 3 weeks old. While she was in the hospital I pumped milk for her to be fed by bottle and with me occasionally breastfeeding with a nipple shield because she was unable to properly latch since she was so tiny. She has just reached 5 lbs. I've fed her with a bottle (fast flow nipple) in the hospital and since she has been home because she needs to gain weight and breastfeeding alone makes her tired very quickly before she could get her fill. She has finally latched without a nipple shield but gets extremely frustrated and takes it out on my nipple because she prefers the bottle. How can I help her transition easier between the two without having her to stop bottle feeding altogether since she still needs to gain weight. Her due date is May 28.