She knows Ben is not targeting her - she watched him nominate and he did not nominate her. She knows Michael nominates her - she watched him do it and was even hurt by him saying everyone hates her but she refuses to let their behaviour change who she is or make her sink to their level.
Actually, we know that she was suspicious enough to hold one of her two 'listen in' privileges to the bitter end in order to hear if Ben's relentless backstabbing of her extended to his nominations (it had on other weeks but not on that one) .
Michael has voted for Estelle six times and allocated her a total of ten points over the whole series so far, Ben has voted for her twice and allocated five points. If I was listing her top six threats, as far as nominations went, Micheal would be number three, Ben number six . Her biggest threats by far are Layla (nominated her 5 times for 23 points) and Angie (6 times for 15 points).
Ben is Angie's number one threat (nominated her 5 times for 8 points total) and Layla's number one threat ( nominated her twice for a total of 8 points - threats to Layla are not that large), so maybe Estelle was not interested in Angie and Layla's votes because she knew their habits and really wanted to know how Ben, the enemy of her enemies, voted. Estelle is a very smart and self-controlled strategist if that is the case.
I think the listening in power might have misled Estelle: Micheal said he decided to vote for Estelle because he had a gut feeling that everyone else would avoid nominating her while she had the superpower, which apparently was the case (Surely it must have occurred to him that there was a risk he would be identified as the one person still nominating Estelle, if his gut was correct, but there you go) . So Estelle might overestimate the threat Michael poses her, or underestimate Layla as a threat to her. As she said, Hate is a strong word. Estelle has become Micheal's number one threat, but none of the boys have ever voted for Micheal, nor Layla, so Estelle would need a strong dose of good luck in addition to all her precious points, to get Micheal nominated before she was evicted. After she was evicted, she might stand a faint chance of getting Micheal out if she gave her superpower to Stacey, but I don't think it is very likely to happen.
Ben has even fewer threats that Micheal - only Layla, Sam and Estelle, in that order. But Sam can be relied upon to target Ben (and be targeted by Ben) so maybe there is some strategic value in Estelle throwing some points Ben's way because of that. I think the obvious target for Estelle should be Angie - Angie nominates Estelle nearly every week, and is nominated herself nearly every week. Sam could help Estelle neutralize Layla, and the three of them could gang up on Ben. But I don't think Estelle is a great strategist, or has any plans like that.