If you ask me, Brittany/Sam are a lot more like brother/sister than Brittany/Artie, probably because of their looks, but still...
I don't know Heather Morris, so I shouldn't really try to figure out what's going on inside her head, but she seems quite impressionable, she will probably always find arguments to ship Brittany with whoever Brittany is currently dating, she found arguments for Bartie while they were dating, she found arguments for Brittana while they were dating and now she finds arguments for Bram. If I were in Heather's shoes I would jump at any opportunity to ship Brittany with another girl, since it gets her a lot of cred in Hollywood, (like what Naya does when supporting Santana's lesbianism,) but Heather doesn't seem to be into that, she only thinks about how she wants to play Brittany at the moment.