AITAH for using my sister's charger?

My phone is currently being really strange with chargers and only accepting certain ones.

I went round the house asking people to see if could test if their charger works with my phone. The only one that works to my knowledge is my sister's charger. She got this charger from a Meta Quest VR headset for christmas (not the last one, year before) and uses it for her phone as well.

I asked her if I could use it while I figure out what to do with my phone and she was perfectly fine with it, and I gave her my charger which works on her stuff, and is even faster than hers.

Then a day later my mum barges into my room demanding the charger back, I explain that my sister was perfectly okay with this arrangement and she even came up to defend me.

Mums argument is that since my sister didnt pay for the charger/headset and was a gift from them it isnt her decision to give it away.

So reddit, AITAH?