Was the wife a ''gold digger''?

They have a poor relationship. It doesn't mean that she's a gold digger.

No, very obviously no. Throughout the movie you see that their marriage has become strained over the years. It's hinted pretty strongly that Gerald has been having affairs while she looked the other way, and can not get aroused anymore without Viagra or the rape fantasy. Pretty common for men who watch porn, they end up with ED and can't become sufficiently aroused by a real flesh and blood woman anymore and whatever sex life they do have becomes more and more colored with the kinks and non-organic sexual appetite they've grown into over the years. This obviously created dysfunction and distance between Gerald and his wife. Men like that usually aren't able to please a woman sexually anymore either.

If you notice later in the movie there's a flashback to when her father is molesting her during the eclipse and the same song is playing in the background as the song that plays during her and Gerald's drive where he reaches for her leg. I think subconsciously she pulls his hand away because it triggers that uncomfortable memory. It's pretty obvious she is the only one trying to hold their marriage together and bought her new nightgown and chooses to allow him to indulge in his rape fantasy. I think all signs point to that she does indeed love him and wants desperately to make him happy. But it's clear he's a high-powered lawyer who doesn't value family life as much. The coroner even says that his fatal heart attack was "a long time coming". A gold-digger would be all too happy to live a separate life with their own affairs and allow him to do as he pleases without feeling hurt that he "hasn't touched her in months" as she says.
I know your post is old and obviously from someone who doesn't care about the story, and probably doesn't even care about the question you asked. But I'm putting this here for others who like to seriously discuss movies.