Request player level up in a specific class?

If you're playing in the Darkwater Campaign with a deaf ranger, don't read. Spoilers ahead.

Context: I am running a game with a cleric/fighter multiclass. She has 4 levels into cleric and 1 into fighter. On the next level up, she plans to put it into cleric to get 3rd level spells and then start leveling fighter. If she does this, she'll get access to remove curse. Now usually this spell wouldn't come up all too often, however one of the players has attuned to a cursed item (unbeknownst to them). For plot, of course, it's not a gotcha thing (actually saved their life, they just don't know that it's draining the life of an npc every time it does so. I need the player to continue attuning to the item for the plot, and so the cleric being able to end the items attunement would be disastrous for the plot.

My options:

1. Don't level them up. Since I control the level ups, it would be easy to just not level them up. Cons of this option is one of the other players really needs the next level up to become useful in combat (somewhat poor decision making in character design, but we've discussed this and I agreed to level them up fairly quickly to compensate.

2. Have a conversation with the cleric. Ask and explain that I don't want them having 3rd level spells yet (no one else in the party has 3rd level spells, so it would be believable that I am thinking that the power of 3rd level spells would break the game. Problem is that it seems a bit... overbearing and manipulative to say, if you don't put your next level up into fighter, you won't get a level up. Even tho I wouldn't say it like that, that's kind of what it boils down to.

3. Level them up, but don't have remove curse remove the attunement. This option is my least favourite but I thought I'd mention it in case someone in the comments thinks of it. Obvious problems are that it's removing a spells explicit function. Which is just not very cool.

4. Level them up, and let it remove attunement, but rewrite the plot. This is probably second least fav option, as I don't have much time within which to rewrite the plot.

Thanks all for your help!