Aksha can spam Darkness, which is a concentration spell

Yeah, also noticed this - second time I fought her she covered everything in darkness, wherever I moved.  It really makes a huge difference to combat difficulty - I also commented on this myself elsewhere. For me this kind of negates the point of the 'pools of light' from the windows.  

Does torch or light spell work in these areas?

Dancing light and the natural light coming from the windows did not have any effect on the darkness for me

correct as only magical light can deal with magical darkness. so if you don't have any spell casters you have to get her to come out of the areas of darkness. if you do have a spell caster, daylight, faerie fire, and in a pinch, guiding bolt all work. Also, cantrips are not strong enough.

I also noticed that she can do multiple of them, which may be a power of hers...
she could be using something like the Dual-Focused feat (Tal'Dorei Campaign Setting, Matt Mercer, and James Haeck, pg. 108).

Fair. But it was a hard fight for a fully rested lvl 3 party honestly.

Ahh yeah, I had that problem when I ran the game the first time, but if you never skip a fight, and do long travel, you can be level 4 or 5 when you have to fight her which isn't so bad.

I suspect it is a bug more than a special power, especially since your options to negate magical darkness are (0?) at low level. I have nothing in my 4th party  - the expected average level I think - that works, and faction limits mean you can't simply buy a scroll that may help before leaving town (in most cases). I did kill her (hooray for magic missile and some lucky guiding bolts/smites) but I feel that something is broken in that encounter - the pools of sunlight etc all suggest some expected tactical element, that she immediately elminates. I have also never been able to break the boards in her chamber, with with firebolt or weapons. And looking about the forums people have quite varied experiences - with vamps not moving upstairs,as if the sunlight was there and so on.

Yeah, sounds like something developers should take a closer look at.

You should be able to negate it with a lvl 2 or 3 daylight spell, and work around it with faerie fire and guiding bolt.
Also, magic missiles will always land, so use this till you cant.

plus you can lead her out of darkness, as they are stationary spells, if she leaves the area that its in you can attack her like normal.

You can lead her out of the darkness, but then she just casts it again at will without having to drop the previous ones.  You can cast Faerie Fire, but with an INT 20 mage spending every spell slot on it over multiple fights, I have never seen it land.  I'm hoping that is just terrible luck.  You could cast Guiding Bolt, but good luck getting that to land in the first place.  You could ready an action to attack when they step out into the light, but since the readied action does not seem to actually happen till after they are done, they have already attacked and teleported/disengaged back into the darkness before you attack them.  

Not saying it's impossible, but damn that fight is a nightmare.  

Update: I FINALLY got Faerie Fire to land on her!  But, it doesn't matter because the darkness imposes a disadvantage roll regardless.  

When I got my faerie fire to land I didn't have a disadvantage... but if you upcast the faerie fire it should be able to work (for dnd 5e).