I told my cousin i would give her 40 dollar body spray from Victoria secret

Shes 12 n i was buying some perfumes and i said i would give her one but eventually changed my mind as:

1. Its my money that i worked for
2. Shes 12? Why is she needing Victoria secret body spray

Shes now salty at me for it and has gone into the bathroom at the mall im at. What do i do?
I know i fucked up telling her yes then changing my mind but i thought it through later and i didn’t want her to have it

i gave her a perfume after posting about it in a different sub but She now wants the other one (the bigger one) but the one i gave her was giving me a headache. Shes even madder now