i'd say the big estate agents aren't great for short term lets, when they offer them they'll be very expensive. i'm in the same situation right now, i'm looking for about a month in NY and it's not easy ush:
for london i'd look on gumtree.com and see what shows up, it is like craigslist though, so she should be careful.
for london i'd look on gumtree.com and see what shows up, it is like craigslist though, so she should be careful.