Hey, @Coriel_Muroz ---I've not been around much, and I realized I had not followed up on this issue of yours.
Now that I read your original question again, one thing I think we all missed is that you were looking to have Nina go steady with the other person, and (I assume) get engaged after that.
In an unmodded game, only teenagers can go steady. However, a MATY-associated creator, syberspunk, made the most commonly used stand-alone mod to enable adults to be able to Go Steady,
here. So if you don't have that or a similar mod, it's normal for none of your adults or elders to be able to Go Steady.
So if you're usually able to see the Go Steady option on your adults, I'm guessing you either already have that mod or that you perhaps use Inteen, which I believe also includes going steady for at least adults. I don't know whether Inteen also enables elders to Go Steady or not; I believe but am not completely sure that syberspunk's version does (been a while since I had two elders I wanted to commit; you could read through that thread I linked or read his documentation to confirm). So it's also possible that Nina couldn't go steady because your mod that enables going steady doesn't enable it for elders.
Back to the glitchy dead-romance thing, which I still think is more important: I suspect that if you used the Blender to allow Nina to date the other sim, that's already removed the commitment to Daniel that the game thought meant she couldn't get engaged to anyone else---which also would support that the dead-romances thing was the problem preventing Nina from having the engagement option.
So hopefully you haven't already put a lot of effort into testing elders vs. adults---because it's very likely the issue doesn't have anything to do with age stage. A better test would be to find or make another sim, preferably an adult or YA, whose former partner has died. If they also can't get engaged to a new sim, then you've proven that it's not an elder thing and that it's the dead-romances bug. And if they *can*, then possibly Go Steady just isn't enabled for elders in your game by your mod that *is* allowing it for adults.
*Ongoing TS2 informational projects (come on by to contribute, get info, or spectate!): (1) the
SimPE Preservation Project and (2)
Conflict Tracking for the 3t2 Traits Project Mods
*Need a Pescado mod? Use his
hack directory: in the first post, find the link for your latest EP, then go in hacks/