Regardless of what she says I would tell her that you understand how she feels but that you need some time to think about it.
The last time the D word came up (7/30) at my house, I told my H I understood how he felt, which made him even madder and he told me I did not. I would definitely not commit. Maybe saying I understand that you feel that way or I apprecaite that you feel that way would work.
We do remind people that the LBS won't find the "perfect words" or "do the right thing" to make it all better and save our Ms.
Having said that, it seems a fairly acceptable understanding that saying, "I know/understand how you feel" will result in the "no you don't" response...
Where saying, "I understand how (or that) you feel that way" is actually believable and acceptable validation language. We aren't saying we know how they feel, because contextually, we may not. Even IF we have had similar feelings. What we ARE saying is... we understand that what ever feeling the WAS is having, it is theirs, their right to own, and acceptable... that sentence DOES validate...
Just realize the WAS may not hear it the way we say it...