Basically she's been hired to BOTH:
1. Extract essential "tribal" knowledge from these people who will retire in 10 years.
AND
2. Make them obsolete.
This is an inherent conflict of interest. It's no wonder it's going badly.
Most likely, Bob feels threatened by her not asking him questions anymore because if she doesn't NEED his tribal knowledge, maybe he won't make it another 10 years.
If it were me, I would try to start plotting out my timelines in a way that makes their retirement date a target goal for completing the transition. And also very politely remind them over and over that they need the company to survive beyond them to pay their retirement, so it's in their best interest to help it move forward and survive beyond them.
A Gantt Chart is a form of timeline that starts at the end and works backwards. You see it a lot on real estate shows.
Rehabbing or building the house has to be done by x date. Plumbers have to be done by y date. After the plumbers, you hire people doing finishing work like wallpaper. Etc.
So I would plot out what needs to happen first for the next step to happen and put everything in order and make it clear these guys are essential until their retirement date and "we appreciate them cooperating in the transition."
I know it's bullshit now. I would say it ANYWAY.
"We appreciate your cooperation. We can't do this without you."
Notice how that first sentence is predictive and doesn't necessarily say they have COOPERATED so far.
My patter would become "We are planning for the retirement of Bob and Co. We know they want the company to survive beyond them so it will actually pay their retirement benefits. We need to be prepared to survive and thrive without them on X date. This is the plan for making the company both modern and able to live without these currently essential personnel."
Anytime Bob or any others in this core group of people expected to retire in a decade decides to trot out their "I'm the biggest asshole and you can't do anything about it." routine, I would reference the need for the company to survive beyond them because it would be sad if Bob had to keep working here past age 65 or get another job sometime before then because the company failed to modernize and can't survive the competition.
Also, I might try to make sure everyone is adequately hydrated, recently fed etc. before any meetings and do all in my power to mentally chalk up bad moods to "Old people need to tend to their health to not lose it."
When tempers flare, call for a break and order a round of pizza or something. Say "We can get back to this question after lunch." or similar appropriate language.
Try to not say out loud "You're old and cranky and need a cookie." But certainly THINK it regularly.