The first element relates to the real reason why it is that Lynn looks for reasons to hate and defame a reasonably caring mother perplexed by a one-sided feud. As she says in her biography, she came to the conclusion that her mother never said good things to her because there were no good things to say so being bad made Lindy feel bad. It's like listening to someone whose kid has an allergy to something screech about you hate her and her child because you don't and you enjoy a food her family can't have. What someone says or doesn't say has nothing to do with what's real but you can't tell someone with an in-built sense of self-loathing that. This is why April never seems to remember that Becky isn't actually trying to destroy her and steal things from her. The need to project her hidden fear that she should be destroyed and have things stolen from her because that's the only explanation a child can give for the way she's treated onto Becky's blank canvas will win out over the evidence of her senses every time.
You also can't accuse such a person of having any sort of negative tendency. As we saw when Jim struck that chord, April was and probably still is transfixed by binary thinking and the slippery slope fallacy. The idea is that if she were to admit to feeling insecure and jealous of Becky, it only stood to reason that she would thus have no positive qualities at all and be a monster of vanity. This insane question-begging and love of the slippery slope fallacy leads to her denial of what her actual feelings and motives are. Since she cannot own negative feelings because of a simplistic and rigid world-view, her feelings of disappointment and loss have to come from the outside.
Finally, we have to remember that she's so in love with any sign of being thought well of, she can embrace the Devil himself if he says nice things to her. Gerald only started to be a bad person when he took care of business and hung out with someone going places and stopped feeding her ego and not when he side-stepped how he thought Shannon and the other special needs kids were subhuman by telling April she's cute. I'd like to think that April might grow out of being easily swayed by shallow flattery because of a poor self-concept but given Elly and Kortney, it doesn't look good for her.