Well..I will give you the advice our vet gave us and our REAL life experiences! Many years ago..we had a very strong willed female Dobie..about 12 years old and full of ummm..let's say life! my hubby brought home a full grown female Rottie from the streets of Los Angeles..within 10 minutes of meeting each other..the dobie had..to our horror..layed flat on her back..the rottie! We were horrified because we had NEVER had a reaction like this. Obviously we were very lucky the rottie was so submissive. Our vet..upon meeting the rottie..gave us quite the lecture about 2 females and how how lives would be miserable and how dangerous it was for the dogs! We had.. had numerous pairings of female dogs over the years and honestly..we were much more afraid of 2 males together. We had no choice but to make it work and we proceeded with extreme caution. We NEVER had another problem between the two of them and I just think the dobie let her know..she was the boss. We had that same female rottie when we brought our female rescue sharpei/rottie mix home from the pound. NO problems at all..in fact, they were great friends. So..I guess..it just depends and proceed with caution. Ours were all spayed too. Good Luck!!