I think it was important to her because: 1) She wanted to be married to him, and she's allowed to say what she feels before she dies. As in, even if she ONLY did it for that reason, that doesn't make it selfish. It's what Barry wants too so... 2) Considering that he first proposed to save her life she wanted to make it clear that she wanted to marry him regardless. ETA: 3) @backtothestart02 reminded me of a third point, which is that this is what Barry has wanted forever so she is giving him a piece of that if they can't have the rest.
The idea that Barry would somehow be able to move on because Iris left him a video saying "move on" (and therefore her NOT doing that is wrong) is absurd. Iris made him promise to look after her father and brother, and he did not do that under any circumstance. So why would he listen to her 'last request' that he move on?
And thanks!
