If it is going to double her commute time, that's unreasonable obviously but that's not the only factor.
Consider someone that commutes into the same location from Portsmouth. Already takes them say 1.5 hours door to door. New location completely changes their commute and adds say another 15 minutes due to different tube route.
Now on paper that doesn't seem that bad because as a percentage increase it's only 17% longer. However, that person might be at the peak of what they are able to cope with daily and that tips them over the edge in time.
Ops partner may have her commute time double from 15 minutes to 30, which a lot of people will say that's still nothing in terms of TOTAL commute time in London and that they should just accept it. But if you have built a life around a location and your commute time being what it is, it can be very disruptive to have it double still.
Each case is different. The company could have done an impact assessment as they will know addresses of all employees. They probably did and came to a decision based on a huge number of factors for a company that size. Frankly, anywhere in London that offered good lease terms and size and accessibility was probably on the cards. I can't tell you hell much complexity there is in arranging an office move, not that I sympathise with big corporate animals when they do it. But there is a lot.
Could she not ask for more work from home days? Depends how much she wants to keep working there. You could get her to try the commute out a couple of times and see how much she hates it!

What tube lines would it be
@Scam?
Otherwise push for redundancy. If she gets better than statutory that would be my plan.