A couple of things...
First of all what do you consider "aggression" from her? If she was in a stressful situation would she redirect on the other dog? Also being that she is 2 she is at the age where she will start trying to decide how friendly she wants to be towards other dogs.[2-4 seems to be when they start getting picky if they're gonna get picky] You say she's already picky about who her friends are, I would be worried with a younger dog if he doesn't stay submissive to her you could have problems. usually male and female combos do better/get along better but if she's had some dog aggression issues I'd really be cautious about the next dog I'd bring into the home; you want to make sure whatever dog you get is very easy going and won't mind the other dog it lives with potentially being pushy.
Basically, she sounds really insecure and I don't know how much you want to flip her world upside down by bringing a new dog into the home. Sometimes having another dog around who is confident can help I have a dog who is defensive/fearful of strangers, especially tall men and having a goofy easy going dog has helped her but it can also make it worse because then the insecure dog can always be insecure while it has the confident dog to hide behind. I've seen it go both ways.
In a nutshell I think you just need to be sure this is the right situation, it would suck if things didn't work out and the new dog had to be rehomed.
Seth, CGC & LiLo
♥♥Sofie - Always in my heart. ♥♥