Leah made things difficult because she'd keep thinking of how hurt she'd been when Sam left her for Emily. Even though she now knew and understood about the imprint, she couldn't hide her hurt and she was all bitter about it. She'd drag up memories of when she and Sam were together. She'd also remind the pack of things they'd rather not think about, like Embry's true paternity (neither of Embry's supposed parents were Quileutes, so his biological father would have to be either Joshua Uley, Billy Black or Quil's father). As well, the other pack members just found it awkward that they now had a mental link with a woman - they had to try to filter their thoughts and not go into "locker room" type talk, and some of them found female perspective memories/thoughts to be weird. And she would freak out if she noticed any of them looking at her naked, or remembering that afterwards, when she accidentally phased.