The other part of your problem has to do with both neutering and territory. An unspayed female will definitely grunt and box you and be generally anti-social. You may notice she digs incessantly or shreds your carpet, or chews a lot. You can compare this to human females who get a little testy before their monthly menstruation. This is probably why Dallas was not very friendly when you first got her, and it's very likely that she's at least six months old if she's exhibiting all those symptoms.
Rabbits begin to show their hormonal natures around three months.
Spaying Dallas will alleviate a lot of your problems. It should make her more pleasant to be around and improve her litter habits. Now, since you brought Sarah home, Dallas is likely feeling territorial. That's why she's mounting Sarah. She's trying to dominate her.