It was a fairly small world back then within the CAMC with likely only roughly a maximum of 1,000 total Medical Personnel - doctors, nurses, various attendants, etc - overseas at any given point in time.
As an example, her best fellow Nursing Sister friend was apparently the fiance of Lieutenant Colonel John McCrae who wrote "in Flanders Fields"; whom she thus knew quite well.
At best might have been a couple of hundred - including my Grandmother & although she'd spent considerable time in France earlier - posted in England immediately after Vimy Ridge. Generally, only 12-15 Nursing Sisters were assigned on a rotating basis to the 2 or 3 - out 5 different ones over the duration - Hospital ships which ferried our war wounded back to Canada.
Click image for details of the criminal German
sinking of the Hospital Ship 'Llandovery Castle'
with the loss of 14 Canadian Nursing Sisters.
(my Grandmother happened to be assigned to RCNHS Araquaya,
outbound to Halifax with war wounded, which recovered
their bodies - thankfully, Llandovery Castle had been returning
back from Halifax with only crew/ Medical Staff on board)
BTW, did you know for about the past 6 or 7 years you've been able to obtain your Grandfather's complete WW1 Military records from the National Archives?
It's not all that expensive at about $3 per page but, if you go through a sympathetic Member of Parliament, they pay zip for docs from this source.
I got my Grandmother's a few years ago via a Liberal MP who simply wished to score free points with a constituent.