I'm surprised you're having a problem with this stuff, Flower! Google Centranthus ruber images and be sure this is what you have!

This stuff grows pretty much anywhere, and it's actually been placed on the noxious weed list in some west coast locations and some Pacific Northwest locations. If it is what you have, and if you are truly watering it DEEPLY that often, it may be getting too much water to be happy. Centranthus is pretty xeric stuff! Dig down in 8-10 inches near the plant and if the soil is really pretty much wet that deep I'd try holding off on water for a couple weeks (or more!) and see how it reacts.

Centranthus also normally reseeds PROLIFICALLY, so if you don't have seedlings coming up near it you might want to watch for some seed to ripen this year, collect it, and start a couple new plants that you could use to replace your original plant if it turns out that there is some other "unsolvable" problem with it and it just keeps struggling along!

I would give you the warning that if you succeed in getting a "good" plant going you'll pretty quickly wind up with a whole "forest" of it if you don't constantly pull out the seedlings. And, from a "noxious weed" point of view it would be a good idea, if you do get a big (huge!) plant going if you kind of keep an eye on it to deadhead it before there are too many seeds going all over the place--not just in your yard. Centranthus, Red Valerian, Jupiter's Beard, is something that I wouldn't be surprised at all if it winds up on the Colorado noxious weed list one day. When I was checking to see if it's already there I noticed that there is already one county in Wyoming, on the Colorado border, that's having a problem with it--tho it's not yet "officially" on the Wyoming noxious weed list.

"Abuse" it a little and it'll probably thrive for you,
Skybird

Here is a link that might be useful: Some New Mexico xeric plants!