I would point your wife to reading about NRE and the destructive manifestations it can have. Also, I would suggest she read about chemical love-the reality of what she's going through is-it's not "LOVE". It's her body being flooded with a bunch of feel-good chemicals, like CRACK.
Not to say that love couldn't develop at some point between her and this woman, but love isn't filled with the need to rush-it's confident and contented.
I agree with Galagirl's post above-100%, so I won't repeat it. But, I will tell you WHY I agree.
I am polyamorous.
I married under a monogamous agreement.
My husband was... neglectful and emotionally abandoned me in the first several years of our marriage.
(there were reasons-those are not pertinent here-but you can read about them if you wish in my blog)
I had an EMOTIONAL (not sexual) affair with my best friend (of 10 years at that time).
Later (couple YEARS), thinking the marriage was over and "why bother waiting it out" I consummated the emotional affair with a full physical and sexual affair.
The resulting disaster nearly destroyed ME.
It nearly destroyed my husband.
It nearly destroyed my lover (best friend).
It nearly destroyed my children.
The consequences were NOT WORTH the gratification EVEN THOUGH the situation I was in was certainly one that most people would have understood me filing for divorce.
The clean-up, the trust lost between EACH of those people and myself (including my KIDS), the years of re-earning that trust-EVEN WITH MY LOVER (best friend)... it just isn't worth it.
However, waiting long enough to be honest and upfront, to uphold the truth of your principles and be forthright with everyone who is directly impacted by your actions-
DOES NOT IN ANY WAY REDUCE THE ENJOYMENT of making mad passionate love with a new lover.
The consequences of waiting are positive. Because you keep your self-respect, honor and the wait will make the consummation that much sweeter.
The consequences of not waiting are all negative. Because regardless of how great that night feels-it will always be tinged with the resulting loss of trust-between you and your wife, between both of the ladies deep down, between the other husband and his wife.
"Love As Thou Wilt"