The ぬきに/ぬきで (抜き) means without.
The whole sentence is basically saying "All flattery aside, she is a wonderful person." ( She truly is wonderful. I am not just giving her undo compliments.)
お世辞ぬきで=without flattery (= all flattery aside)
冗談ぬきに=without kidding (= in all seriousness)
Hope this helps, maybe someone else can give you more info. ^^