Mareo, it is a good idea.
Just sit her down and tell her how you feel, and that you want to go. Her reaction should not be a reason not to say it. We all have to be mindful of each other, but not to the expect of hiding how we feel in case our partners dont like it.
Wouldnt do any harm to check out Relate local place of meeting, costs etc, so you are prepared and can move on it, if she is agreeable. We discussed it ages ago, twice, but didnt go, and we were sorry when we did eventually go that we left it so long, as it was very very helpful.
Personally, I think that a sexless marriage is a disaster and needs fixing, unless both partners are happy, which is unusual. And it is reasonable to be grateful for a gift.
She probably has issues too but it is her responsibility to raise them, NOT yours.
My h didnt raise issues until we got to relate and we agreed that wasnt fair of him. not that he had wanted or could be bothered to, given his interest in other women at the time