>Is there any evidence that the flower-selling industry is responsible for creating Mother's day, or at least for pushing it to the popularity it has now? 

Yes.

In the USA, the current Mother's Day holiday was [enacted by a joint resolution][1] of Congress on May 8th, 1914.

Prior to being made a federally recognized day, florists did play a role in promoting the idea.

In the August 1910 [Proceedings of the 26th Convention of the Society of American Florists][2] it is recorded Anna Jarvis's attempt to create Mother's Day "has proven so beneficial to the business" and a unanimous resolution was passed to publicly recognize her efforts.  

In the 15 May 1913 [The Florist Review][3], volume 32, page 17, there is an article LESSONS OF MOTHERS' DAY:

>Chief of the lessons of Mothers' day is that of the power of publicity; second, the effectiveness of concerted effort.  

> **The florists made Mothers' day. But for the florists the lady to whom we are indebted for the beautiful idea would never have got anywhere with it.**

>Mothers' day has made progress just in proportion to the push the florists put behind it—where the florists sat supine, there Mothers' day is practically unknown

Only the following year was Mother's Day federally recognized.  

  [1]: http://www.archives.gov/historical-docs/todays-doc/?dod-date=509
  [2]: https://books.google.com/books?id=73o1AQAAMAAJ&pg=RA3-PA140&dq=florists%20%22anna%20jarvis%22&hl=en&sa=X&ved=0ahUKEwjiiJC9tsXLAhXIGx4KHYa2DUEQ6AEITzAF#v=onepage&q=florists%20%22anna%20jarvis%22&f=false
  [3]: https://books.google.com/books?id=U8k9AQAAMAAJ&pg=PA17&dq=florists%20%22anna%20jarvis%22&hl=en&sa=X&ved=0ahUKEwjiiJC9tsXLAhXIGx4KHYa2DUEQ6AEIRDAD#v=onepage&q=florists%20%22anna%20jarvis%22&f=false