Very little in the U.S.  The country is so hard-wired against heavy women.  The subject website has an America link that may be worthwhile for her to advertise - I think there is a message board too.

TER.  Once she is reviewed here TER search will show her suitors the way.
Behind closed doors there are more guys with lust for BBW than publicized.
 I've seen it with my own eyes.
I've never seen a legitimate site catering to one type of woman. Doesn't mean they aren't out there.

I highly recommend backpage. I shop on that site for thick/bbw type women and have had good success. Fun to be with dick deep in the pussy and balls deep in the ass checks.