Amabel hasn't hurt anyone, especially Philippa, and yet the other person was very stubborn and wanted to cause trouble. She felt troubled and in pain, because someone she has done so much for, loved as her own sister, even more than a sister didn't see her as such. Her words were very painful, and at the same time, she couldn't help but waver.
A relationship of over a decade wasn't something easily discarded. That's why even when Philippa was in the wrong at the shop, she couldn't help but waver and not react quickly. Even now, when feeling happy for Amabel, her thoughts strayed to Philippa.
Philippa wasn't perfect, and neither was she. That's why, all these years she could tolerate her imperfections. That's why, despite knowing what they were doing was wrong, she still helped Philippa to trace all those girls Valentine was seeing, and provided her with information she could use to chase them away.
