Soldato
Maybe there is some financial problems your sister has and she told your mother, and then asked to keep it quiet because she didn't want to be embarrassed in front of you?
The point I'm making is she might not have lied to undermine you. But she didn't want you to think bad of your sister.
This is assuming your sister hasn't been lying to your mother giving her a sob story and didn't want you looking into it.
I doubt your mother lied to you for the hell of it.
If I was you I'd be trying to find out why she lied about it. Ask her what your sister said to her. Then ask your sister separately to see if the stories add up.
The point I'm making is she might not have lied to undermine you. But she didn't want you to think bad of your sister.
This is assuming your sister hasn't been lying to your mother giving her a sob story and didn't want you looking into it.
I doubt your mother lied to you for the hell of it.
If I was you I'd be trying to find out why she lied about it. Ask her what your sister said to her. Then ask your sister separately to see if the stories add up.