One of my favourite characters was destroyed in a dodgy mod uninstall, so I'd like to try and recreate her!

Orsimer - Female - The Mage

Blunt
Heavy Armour
Conjuration
Destruction
Alteration
Restoration
Mysticism/Illusion?

I'm uncomfortable with having 3 Willpower skills as Majors - I inititally wanted to lower Restoration (it's pretty bad for healing in my opinion, and I generally use it to 'top-up' rather than truly heal) but it takes bloody ages to train.

For a seventh skill, Illusion could be useful for gaining access to Charm magics to deal with being one of the pariah - a female Orc having the lowest personality in the game. Mysticism is always sueful for a variety of things, but perhaps difficult to justify as a major.

Armourer and Alchemy are kept as minors due to how easy they are to level and the ease of then training Endurance and Intelligence.

Drop Alteration to minors. It's easy to train to 25, which is all you really need unless you're planning to use it for opening locks. I rarely put Conjuration in majors since I use it a lot for collecting souls and it levels really quickly. You could keep both Illusion and Mysticism as majors.

Mara

I would go with illusion, because if you want to bypass some enemies you can turn invisible.

Plus, Illusion would help raise the Orc's low natural Personality trait which may be desirable for some builds. It depends on what your goals as a player are. A true Battlemage build would always use Destruction since the lore of Battlemages teaches this is their primary means of attack, but you're free to be flexible and create the character that meets your own gameplay or roleplay needs.

I really like illusion, it has a vanilla high casting value but its spells from charm, command and pacify to invisibility make it very useful.
I also find it does not level up as fast as mysticism if that is another concern, and finally mysticism spells tend to be of most use on enchanted item imo.
With any armour I would however drop destruction unless you just want the stat increase, as whenever I use the combi the spells tend to be next to worthless.
Try marksman instead as a higher agility boost you get will bring will stop you getting pushed around in combat as often, which is vital for a up close characters I have found...
But each player has his / her own style, so just go with what feels right to you.

Orcs are not exactly the best mages............

It only matters in the beginning of the game really.

Illusion and Alteration usually level quickly for me. I would dump those too, and pick up Athletics and maybe Block. The reflect spells at higher levels for a Mysticism major, I believe, are needed more than the Illusion offensive skills. Besides, aren't you using a blunt to deal the killing blow? That is, don't forget about your weapon as a part of your killing package, as you think of your skills.

I would drop alteration and take illusion, provided you really make the most out the command spells and get custom spells early on. you could also drop conjuration but truly if you use command and frenzy to start fight then finish the last enemy with ye ol' axe, you will be so powerful that leveling is not going to be an issue, and you won't even need the fancy +5 modifiers...

You realize that a Battle Mage usually carries a weapon, right?