Introducing two female dogs

A friend of mine recently found a young dog. She is going back and forth about whether she can keep the dog. A friend of hers has expressed interest, but my friend was concerned since this person already had a female Boxer, and she was unsure about whether two female dogs can get along together.

I couldn't help her much, since in all my life when there were multiple dogs around they were always mixed male and female. My sister has two females, but they are both very "soft" dogs, and the two dogs mentioned above are Boxer and American Bulldog.

What has been your experiences? Would this be a good match? I'd like to encourage my friend to find another home for this pup, since financially she might have a hard time caring for two large dogs. Oh, did I mention that this pup just went into her first heat, and my friend's male dog has not been fixed yet? Geesh!