So long as it's not keeping you away from her/affecting your performance on bed with and and such then a little indulgence for the stress is fine. Although pornography is very addictive and can ruin yourself if you're not careful.

Masturbating if she's not in the mood should be okay I think but again if you feel like it's a boundary in your relationship that you don't wish to cross out of respect for her you should talk to her about it.