I have been told to 加油 by a Shanghainese 阿姨 because I was 30 (at the time) and haven't got married (she couldn't understand why with such a choice from both Chinese and international communities, I couln't find someone).
But this goes way out of the scope of this thread, customs of people concerning heart matters here are really different from what we are used to in the West, so sometimes even the easiest, blandest ideas are not to be expressed in some contexts, whereas we would naturally express advices and opinions in the West.
After reading your post, something just popped into my head and I would like to share with you guys.
I believe that in China people sometimes use "jiayou" to express his or her slight dissatisfaction or dissapointment.
ATTENTION: the level of dissatisfaction or dissapointment is so slight that the whole sentence is not at all negative.
When I was a kid, I could not remember how many times that my parents and my teachers used to tell me that I should "jiayou" because they thought that I wasn't working hard enough, my grade was a little bit low to their expectation, I was spending more time in computer gaming etc.
They would say something like
"Look at your grade, you should "jiayou" blah blah blah."
Because that I am from the region of Shanghai, I could imagine the scene in which the Shanghainese ayi was saying that word, I might be wrong though.
In your case, mon ami, wether that shanghainese ayi is dissapointed a little or she simply wanted to encourage you is not determined. It all depends on the context, intonation, and stress/accent. But anyway, a lot shanghainese ayi should really mind their own business.
