I found my step-daughter’s USB memory card in my bag. She must have dropped it in there accidentally. I asked her in the past “What is on this USB memory card?” and she replied saying “Its stuff for college and photos of movies I like”.
So I believed her. But then recently she said “I am struggling at college. Can you help me?” and, obviously, I said “yes.” So I helped her as much as I can.
Today when found the USB memory card in my bag that she accidentally dropped, I had a look on it to see if she is still struggling.

OMG!! It didn’t JUST have her college work and photos of movies she likes on there. There was also had explicit photos and videos of her and I was in shock to see that. So much that I was shaking, sweating and my heart was pounding.
I am not to sure on what to do.
A: Do I just keep it as a secret and not tell anyone what I saw and just give it back to her?
Or
B: Do give it back to her and try to explain to her why it is wrong to take explicit photos and videos of her self?

Reasons why I can’t make up my mind, cause if I do:
A: She might think it’s normal to take explicit photos and videos of her self and carry on

B: I will lose step-daughter’s in trusting me

What shall i do?