"An issue which is often forgotten, but which is important, is copyright. Copyright always rests initially with the artist, but can be sold or assigned to someone else, as an entirely separate commodity from the original artwork. All changes in ownership of copyright must be done in writing and signed by the artist, otherwise they are not legally binding.
Copyright remains with the artist so he or she can earn money in the future from sales of licenses in the image. If your commission is for a neutral subject, then this should not be a problem for you. However, in the case of portraits, most people would prefer for their image not to appear on merchandise. In this case, you need to arrange, at the outset, for copyright to be transferred to you. The artist is under no legal obligation to agree to this, but, so long as you discuss the matter before the artwork is created, you can always take your business elsewhere. And most artists should understand your concerns. It is quite common, particularly among famous people, for such a contract to be made.
Prior to August 1989, when portraits and photographs were commissioned, copyright rested with the person (or organisation) who commissioned the work. This is no longer the case. So, in theory, an artist or photographer can now sell your portrait or wedding photographs for any use they wish, unless you make a contract stating otherwise."
I am not sure she is allowed to post the photograph though, I think she needs a signed model release form for that but I could be wrong.
If it's on Facebook, you can try asking them to remove it if your child is under 13.
"The following content may also be removed [from Facebook]
A reported photo or video of people where the person depicted in the image is:
A minor under thirteen years old, and the content was reported by the minor or a parent or legal guardian
A minor between thirteen and eighteen years old, and the content was reported by the minor
An adult, where the content was reported by the adult from outside the United States and applicable law may provide rights to removal"