I don't know how you managed to beat floor 90 with that team last time.
If you post the roster of your champs, we could try to find a better team. Your actual team has 3 revivers, but it has no champ that can remove debuffs. I'm not surprised that you can't beat the Nether Spider with that team, it lacks the most usefull mechanic vs. Nether Spider.
Do you have Reliquary Tender (rare, High Elves)? Her remove debuffs can be booked to a very fast cooldown. If you don't have her, the campaign-farmable Medium could help as well. But her debuff-removal has a longer cooldown.
/edit:
Thinking about it I have an explanation why you could beat floor 90 last time. It's the affinity!
Drexthar has force affinity, the floor 90 Nether Spider of rotation 1 has spirit affinity. The Spiderlings will allways attack Drexthar, because he has weak affinity, so it's easy for him to put hp-burn on all Spiderlings.
In the actual rotation, the Nether Spider has magic affinity, Drexthar turned from weak to strong affinity and will not be attacked. If you use his A2 to provoke the Spiderlings into attacking him, they will do a counterattack to his A2 and heal the big Spider.
2 ways to solve this problem: Either remove Drexthar from the team or use a champ that puts a 100% heal reduction on the big Spider, so that Drexthar can use his provoke move on the Spiderlings.
