I actually liked Selyse a lot. I find her a very sympathetic, tragic character (much more so than in the books, to be honest).
Tara Fitzgerald (apart from being extremely pretty) portrays Selyse as a broken woman, who, stricken with grief over the loss of three of her children (and a near-death of her only surviving one) and married to Stannis - a cold and distant man, never intimate with her and uncomfortable in her presence - is only capable of coping with her situation through religious fervor.
Selyse keeping her stillborn children preserved in glass in her own bedroom is morbid and disturbing - but, as with Lysa, her excentrities are the result of a terrible past trauma, the failure to make justice to what they perceive to be their defining responsibility - to produce an heir to their husbands - and the fact that they had to face it alone.
It’s quite unfortunate that, judging from her tag, she will probably be remembered primarily as the crazy-fetus-lady.