You should tell her what you told us and see what her explanation is. If she is forwarding you a nude photo she must tell you why that's the case and who she forwarded it before you.
Also it's a question of boundaries, if she is texting another guy and talking dirty to him she is clearly crossing the line. Why are you tolerating it?
Don't cry, don't regret and don't blame
Weak find the whip, willing find freedom
Towards the sun, carry your name
In warm hands you are given
Ask the wind for the way
Uncertainty's gone, your path will unravel
Accept all as it is and do not blame
God or the Devil
~Born to Live - Mavrik~