Women in labor need lots of support. Your partner needs to hear that she's doing well, that things are progressing as they should, and that she really can do this. Even if her mother, sister, doula, and five of her dearest friends are with her, she needs you.
Support means different things to different women, though, and your job is to figure out what your partner needs while in labor and do it.
How to figure out what your partner needs from you
Your partner may not be in a talkative mood during labor, so asking her what she wants you to do may get you kicked out of the room. This is one time in her life when she wants you to think for yourself and take action. Take the lead by offering choices. Ask her whether she wants
A back rub
A massage
A hand to hold
You to sit behind her and support her back
An epidural
You to kick her mom out of the room
Ice chips
To get in the tub
Any of the other labor options you discussed before today
How not to take your partner's insults seriously
Women aren't responsible for anything they say during labor, but you are, so don't get upset over any suggestions your partner makes about your anatomy or her comments on your ancestry. And she doesn't really mean what she said about your mother, either.
Pain makes people say things they don't mean and may not even remember, so don't file away her remarks for another day. Vocalizing the pain in this way is both healthy and normal. Because you're not in pain, you don't get the same privileges, so save the snappy retorts for another time.