I have a new arcane archer, a high elf.
However, she is no friend of the Thalmor. She just killed a few, actually.

Any reasons for her to hate the Thalmor?

Many. Take examples from http://www.imperial-library.info/content/rising-threat, if you wish.

Many, many Altmer hate the Thalmor and the Aldmeri Dominion. The Thalmor are pretty much facist in the sense that they belive they are racially superior to all others and belive that their race has been weakened by non-Altmer blood to the point that they must be "purged" (killed). Many fled, and one even wrote a 4 volume book (The Rising Threat) before being assassinated by the Thalmor. During the war, the Altmer would send raids into refugee camps and enclaves just to kill off those who fled when the Thalmor sized control.

The court wizard in Dawnstar might be worth talking to. She fought for the Empire against the Dominion.

Yeah...that is plenty of reason for my character to give them a black eye.

Every oppressive and tyrannical government has scattered dissidents among its own people.

There would probably be a number of Altmer that don't agree with what the Thalmor are doing for many reasons: friends in other regions,trading disrupted,constant battles with opposing factions and i would like to say because of talos to but i dont know if many Altmer prayed to him to begin with.

Man, the Thalmor must've rubbed a hell of a load of people up the wrong way! I mean, do those guys have any real friends, or just the ones they threaten?

Thalmor: Be my friend...or else....

Thalmor: You want to be my friend, don't you? Doon't...you...(whilst holding a knife to the person's throat)

Even Chadric has made a pledge to destroy them all!

what do you mean even Chadric like thats supposed to be a surprise? Nords....Pffft.





(lol)

but yeah as said the Thalmor don't have any real friends, except MAYBE the khajiit, and only because the Khajiit think the thalmor brought back the moons.

Just imagine how many Altmer who lost their families to the "purges". The Thalmor are good at killing people who disagree with them. And as I understand it, plenty did.

I can think of many reasons why Altmer characters can hate the thalmor. Won't list them all but for one maybe your own character just doesn't have that useless hatred of other races?