Why didn't Anne Sampas become like Eve?

They never explained it. I have a theory that maybe the alien DNA didn't take correctly in her, hence the weird offspring followed by death. Or maybe Patrick was the best match, so he got the "best" DNA and she was infected by whatever was left over.

In reality, it just seemed like the writers had no idea what to do with the character, so they killed her off in a burst of tentacle birth to focus on Patrick.

why didn't we get a nude scene is my question. she was cute.

She did become like Patrick in that she was infected. Patrick didn't know what was going on at first either. She became pregnant as soon as she had sex and the embryo developed quickly like the others. Unfortunately since she was the female, the embryo burst out of her like the other girls and killed her.

Perhaps the writers originally wanted to have a guy and a girl alien-human hybrid as prominent antagonists but thought it would be too much, so went with her just becoming a throwaway character.