And trolls, and goblins.Stormwind was recognized as an Alliance kingdom despite being destroyed and king Terenas himself invited the then young Varian to Lordaeron. Even if you somehow argue that Stormwind was technically not part of the old alliance because Varian was not of age to sign a treaty we still have the dwarves of Khaz Modan who were members of that alliance. Plus I really doubt that when Alleria returns she will start thinking about it that way, she will not care about semantics and technicalities. All that she will see is a horde with the orcs that she hates and blood elves who are probably led by the people that she disregarded when they told her to NOT help the Alliance. She will also be disappointed in the behavior of her undead sister who thinks that raising the dead as forsaken is right. When she looks at the Alliance she will see her people, the high elves, who are unaffected by demonic taint, her living sister Vereesa and the people of her husband.
Tell me who would you choose?
An undead sister that committed atrocious crimes or a living sister?
A portion of your people that succumbed to demonic taint and allied with some of your worst enemies or a portion of your people that resisted and are in the faction that your husband supports?
And are some people really arguing that she was a friend to Lor'themar? Even if she used to be it doesn't matter, she hasn't seen him in years but she has certainly been through a lot with her husband all this time.
There is no way that she would choose a crazy undead sister and a "friend" over a living sister and her husband and that is obvious even if you ignore the fact that they are allied with the orcs.
However, I can totally see Alleria trying to "help" her sister, that much is reasonable and expected but this shouldn't make her a friend to the orcs:P