it's a line of a poem means the matter vanish like spring dream without trace. but in oral chinese,春梦 means sexy dream.......so maybe she wanted to tell ur friend that had a sexy dream......

search on the internet i find it's from a poem: http://baike.baidu.com/view/3053879.htm#sub3053879 meaning(i try my best): it's like a spring dream, when you get up in the morning, nothing has left in your memory.

I'd try my best... Basically it means a wet dream without an ejaculation if you translate it directly. But people seldom use the phrase in this sense in Mandarin. I suggest you use it with discretion.