You partly answer your own questions. You obviously have learned a lot about HPV and I agree with all you say starting with "I feel that...."

Barriers are not very effective in preventing HPV transmission and this approach probably has little value for the excessively fearful partner in this setting. Consistent condom users have a lower risk of HPV for any one exposure, but there is much opportunity for skin-to-skin contact even with condoms, and in the long run consistent condom users acquire genital HPV almost as frequently as those who never use them. It's more important for her to understand the HPV basics as you apparently do:  almost everyone is infected at one time or another, often several times; given her apparent sexual lifestyle, she can be sure she's already had HPV and could be infected at this time; that the large majority of infections cause no important health problem; that vaccination is an option to further reduce the chance of an unpleasant or serious outcome; and that sex with you or your regular partner will not significantly elevate the chance of an important health outcome. It's much more important for her to follow standard Pap smear guidelines to detect cervical infection before it becomes more serious; and to consider immunization. Finally, that most HPV cancers occur when a past, chronic infection reactivates -- and not because of a recent new infection. That is, her chance of a potentially serious HPV outcome will be not be significantly reduced by having sex with your husband.

But a final word to the wise:  I'm sure you understand that swinging groups (if I may use that term for your situation) can be at significant STD risk if and when memberships change, i.e new partners join in. If there is any turnover in your group membership, I would advise everyone to be tested from time to time for gonorrhea, chlamydia, syphilis and HIV. (In other words, not rely entirely on the newcomer only being tested.)