Late reply, but Kasumi probably couldn't get a clear read from Sumika, her memories were all a mess and she was focused on Takeru and her hatred of the Beta. She may have been tasked with getting that information as well as communicating with her, but remember that in UnlimitedYuuko said that Takeru could help her with her work, that is because she realised he had stable memories and Kasumi could get a better read from him, it's highly likely she had Kasumi go do a read on him while he was being detained.
In Alternative she looks at his files and decides there may be something to what he has to say and that he may be useful, but doesn't know what her other self was up to when it came to using Takeru, but Kasumi hadn't spoken with her or taken a reading of him at this point,so it's only later on after Kasumi goes and speaks to her that she decides to trust Takeru and seems oddly happy about it all. I think it might be worth noting that unlike in Unlimited he hadn't been thinking about Sumika or his world until he decided to visit Kasumi.
But Kasumi in both is able to see Sumika from his memories and get a better picture of her from him, also she does say near the end of Alternative that a lot of the memories she picked up of Sumika she got from Takeru and she got happy memories from him of his time with Sumika, so his definitely were the clearest memories.