Her one strength feat I can recall is making that trailer scoot with a kick. Something Colossus and Angel Dust could do with ease.
She's more skilled, but Colossus is imo stronger and way more durable. He beats her down first round. Second round though yeah I think her sword may be able to pierce him.
What has Angel Dust done to suggest Sif isn't "nearly" as strong as she is, and that she could replicate the trailer feat with "ease" (and it's not like Lady Sif struggled to do it either)? Her best feats are sending Colossus flying a couple dozen yards with a hit and pushing him through some rubble, and Sif easily kicking a trailer to send it skidding several yards over the ground is no simple feat. At 36 seconds.
Waded through it like "it wasn't there" is somewhat exaggerating. She was visibly straining with effort when she was pushing him. And a camper trailer like that also weighs a good couple of tons. Fact is that neither she nor Colossus has actual visible feats that put them well above Sif in the strength department, especially considering that Sif didn't seem to be over exerting herself during the trailer scene either.
Though I suppose it could be argued that Colossus was somewhat restraining himself against Angel Dust (he seems to have this old-school chivalry thing going).
My point stands. She doesn't actually have any feats that suggest she is tons stronger than Sif, considering the ease with which Sif can kick a camper trailer and send it skidding several yards. If Sif can shift that much weight with a quick kick, she could more than likely replicate the pushing Colossus through rubble feat if she really tried.
That's speculation though, based on interpreting how much Colossus was holding back, and how much him going all out would make a difference. And in anyways, it's gone beyond the point I was making, which is that Angel Dust herself doesn't actually have onscreen strength feats that put her as far above Sif as some people are suggesting.