Alice de Breton, Mistress of Roger DeBreton

Fitz- is an indication that means someone's child,it is not a surname and it doesn't go to the wife, mistress or anyone the person is associated with. Hence, Alice here is NOT FitzReinfrid, because that'd mean she is the sister of the man whose mistress she was and daughter of Reinfrid, which she clearly is not.

Roger FitzReinfrid was born circa 1114.2 He married first Rohese de Clare, daughter of Richard FitzGilbert de Clare and Adeliz le Meschin.1

Roger FitzReinfrid married second Alice de Breton, daughter of Lewis Brito.2 Roger died after 1198.2

http://www.lawrencefamhis.com/ashton-o/p2573.htm#i64310