[Letters from professor in an unrelated field]

Thank you for your response!

To clarify, I will have 2 letters from within the field of Psychology (I'm sorry I forgot to mention the second!) and am trying to determine whether another from outside of Psychology would be ok for my 3rd. One of the programs I'm looking at requires 4 letters, but most only need 3. 

[Letters from professor in an unrelated field]

I'm preparing to apply to grad school, and I'm uncertain about my recommendation letter situation. I go to a big school, studying Psychology and applying to Clinical Psychology, most of my classes are 100-200 student lectures and unfortunately I don't have many "close" relationships with my professors. I will be getting one letter of recommendation from a club I participated in that I feel will be relatively strong (essentially it was a a year-long club where we participated in seminar discussions and putting together research presentations). Aside from that, I just finished a Sociology class that the professor described as being similar to a graduate level seminar, she knows my work well and has said that she would happily write letters of recommendation. Another professor in the English department invited me to present my research in an undergrad conference that I participated in, and worked with me quite a bit on that. 

So I guess my question is, how acceptable / unacceptable is it to submit letters of recommendation from professors outside of the field you're entering into? Specifically these situations... The Sociology professor is well-known in her field and a full professor, however the English professor is younger and newer to the university and mentioned that that might make her a weak reference if I used her.