Is it okay to have two female dogs living together?

i own a female french mastiff thats about seven years old. She likes other dogs, lives indoors is spoiled&cute and likes to play with the neighbors dog which is a male golden retriever. I want to add a female kuvash puppy to the household, but will it be okay with my mastiff. will she feel sad and replaced. or will she not like a female so should i get a male instead?im worried!!!