Definitely an improvement. I still think that forceful cage is a promised TPK- there is nothing that stops her from locking out the leader or defender with it.
The defense of fortitude would be 40 something: 10 for base, 15 for level, 6 for item, 10 for stat (or so, my guesstimate!)- assuming no feats: 41.
Dweller has a +49, on a d20 she's aiming at 59 or so for your expected value, assuming she is consistently marked, and your party has permanent concealment, that drops it to a 55, your lowest value you can expect is 47 (2+49-4). It's an almost guaranteed hit that can and will let her pick off people one by one. A highly intelligent creature will (should) be able to single out what their greatest threat is, lock it down, take care of the rest.
Teleport 10 means no escape from this creature- truesight negates invisibility as a defense. Her ability to slow/dazed will prevent any kind of defender from functioning as punishment- teleport negates any kind of OA against her, using a swordmage may help but only if you're not dazed.
Here's what I see vs various defenders: let's say AC is 18+ level (that's a high estimate, I think)
Reach 1 type (shield fighters, wardens, swordmages)- are crap out of luck against the Dweller. She'll average 50 AC hits on reactions that don't even need to target him, she can probably take him down by reaction attacks alone. dazed and weakened defenders don't do much damage, and can't threaten much if she can just teleport away to where he can't reach them. Dazing also takes away the immediate action.
Reach 2+ type- even worse unless you have a high dex, against reflex it's around a 49. Most defenders don't have a high reflex, dazed restrained is the most likely combination here.
Battlefield control is nearly useless, sliding, hindering terrain, etc. all not very helpful seeing as how the dweller has teleport and can fly.
granting save ends conditions: not so much, +5 to saves means a 75% chance to save on each effect, in addition to being able to make throws as soon as it occurs. High will makes it even harder to stun/daze her.
However, susceptible to debuffs- a 46 and 47 to reflex are both hittable: +15 half level, +10 ability score, +6 magic item, +3 expertise: +34, so we're talking maybe 60/70% hit rate from the controller. Debuffing (lowering attack bonuses, making it harder for her to hit; or lowering defenses) is your best chance here.
Were I using this creature, I would be locking out the leader. Force cage and other attacks target NADs. Force cage would hit leader each and every time they are free- this prevents buffs and heals for you to drop the striker. If the cage is not saved against the cage would be open to use against another person.
Leaders stack up on save bonuses- end of encounter effects etc. This fight can and will suck for you.
Also I'd go into this fight with 2 leaders, for a standard party of 5.
You'll be my focus if I was this creature. I can ignore the controller and defender, lock out the leader, and focus on you. You will defintely be slowed, playing ranged won't help you much, my ranged 20 with teleport 10 will get to you almost anywhere you go. Going invisible won't help you much either. If you're in melee that's even worse, you can bet on being caught in the blast with the defender every single turn.
Summation of thoughts
In short, this is a hard fight, the reduction of the blast power as a reaction is a good move to make it more "fun". Forceful Cage probably forces this to be a 2 leader fight, be prepared to have one frustrated player. I would again suggest that forceful cage be made into at the very least a recharge on 4,5,6. Countermeasures below:
Everyone in the party should stack on necrotic + cold resist gear, everyone should wear boots of teleportation.
Forgo "save ends" effects for end of next turn effects.
Timely Respite is your friend in this case- it should give you another throw against the annoying force cage.
Using flaming weapons: everyone. Bring a fire wizard, or sorc, everyone should have a reliable way of dealing fire damage.