Well, we know that the gold digger knows the conditions of the other two recipients. Now assuming that it really is Bella, she'll be aware of the fact that a certain point, the MC will have to make a decision about the house and that it's Elaine's condition.
We don't actually know that. We only know that one of the other beneficiaries knows the conditions. It could be Dizzy, but it could also be Elaine. As usual, our clues are incomplete.
If we believe Bella's story, Elaine is indeed the one who knows all the conditions. If we doubt Bella's story, the most likely explanation is that Bella is Dizzy and she's the one who knows all the conditions. I'm firmly in the "doubt Bella" camp, but we won't know for sure for another month.
So why would she want to turn the MC against Elaine? Simple, even if it has nothing to do with her own will condition, by getting rid of Elaine she increases her share of the inheritance by 50%. And if she can knock the MC out of the picture, she'll get the whole shebang.
Why hold on to the video for so long? Because if she knows the will conditions, she might also know the time frame of when the MC has to make the decision. If the MC had the video earlier, he could've confronted Elaine and she might have been able to set him straight. They purposely waited to give you the evidence at the last minute and even then Bella told you to not confront Elaine with the footage.
But why give him the video at all? As is the only reason the MC didn't confront Elaine with it is that a) he completely botched the question when he could ask her in Episode 21, and b) he's too lazy to drive over to her house in Episode 22. Why leave that to chance? Accusing Elaine verbally seems likely to accomplish at least 85% of the effect with less effort and lower risk.
And it's not impossible to deep fake someone's face accurately enough that it might fool some people, especially with a low quality footage. Someone like Jolina, who has shown that she has some tech skills, could pull it off.
I'm going to have to disagree. The MC knows Elaine well, and if she isn't clearly visible in the footage it's useless as a smoking gun. That's not something Jolina's known skillset could easily fake. She might be able to edit footage of Elaine into a different background to make it look like she was at the cafe when she wasn't, but I even that would be a stretch (and it would beg the question of where she got footage of Elaine to begin with).
At a certain point I think we need to trust the overall thrust of the narrative we're given. Sure, technically we have no proof that Greg really is a lawyer, but by now it would hopelessly muddle the narrative to try to claim he was in on the con the whole time. Likewise, we've been told Jolina has some tech skills, but we've also been told she's not up to Jenna's level and Jenna hasn't suggested the footage could be fake. I see no reason to believe either of them could fabricate this sort of evidence out of whole cloth.
I think the footage really is Elaine, though the context could still be misleading. If it turns out to be otherwise, we're going to need a very solid explanation for how that happened.