I think that would be too early - but thanks for looking.
Re-assessing the evidence, the marriage certificate for Mary Short / Charles Broadwood in 1854 gives both as "full" age, putting Mary's year of birth as around 1833 if that is correct.
I got to thinking about one of my first ever roots chats posts:
This photo dating thread, which put the date of the picture at about 1860 and the age of the woman as in her early 20s. If that's correct we're looking at a year of birth between 1835-1840 slightly young for the Broadwood marriage, but managable.
It seems that this lady was married to someone by the name of Broadwood but was a widow by the mid 1870s.
She then married again and became a Bartholomei.
In her daughter's marriage banns in France she's Marie Broadwood Tourmaly Hamilton & in the licence she's Mary Broadwood Hamilton (the Frances has gone, but that could be an easy mistake by Hélène)
I am still inclined to thinking we've got a many-aliased lady here, but it's getting more difficult to link her with Charles - I'd like to find the truth though as she still intrigues me, an interesting lady even if she's not who I thought, and there's not an obvious fit for a Lowther so far. Of course it could just be another alias...