baby momma drama ☹️

Melissa
So my boyfriend and I have been together for 3 years and I'm now pregnant with our first child together. He has a daughter with his ex girlfriend (she's 5 now) and ever since I've been with him she's had something against me.. now that I'm pregnant even more. She uses this baby as a defense when arguing with my boyfriend. 
They didn't end on good terms and it's really difficult for them to communicate. 
I just wish there was someway I could be cordial with her. I don't want her to hate me especially for no reason. My bf was with a girl before me and they got along fine so I don't understand her.. is there anything you gals think I can do so we can be on good terms? We're kinda stuck for a very long time now and I'd like it to be a good relation..