If this guild is giving you something, then by all means continue to attend. As for big mouth....
When someone continuously criticizes or finds fault, it's not you that they are finding fault with...it's themselves. This woman has an over abundance of low self esteem, and in order to build herself up, she puts others down. She obviously lacks self confidence in her own abilities or she would show her work.
Don't let her pull you down to her level by making you question your talent.