That's a Camellia japonica. They do best with some filtered shade or protection from the afternoon sun. Camellia benefit greatly from a 2 to 4 inch layer of mulch (bark or pine straw) in a large radius around (but not piled next to) the trunk.

Any ideas as to why the plant isn't doing so well right now? Perhaps you could take images of the symptoms or describe the trouble.

Unless you know your soil is high in magnesium, you could try applying Epsom salts - a hefty teaspoon to a gallon of water poured onto the root area after it's rained.

If your soil has been hit by weed spray or ruthlessly groomed of anything looking like humus by the previous owner - mix up a catcher full of lawn clippings with some compost (NOT mushroom compost - too alkaline) and spread that on the soil to about three inches deep. Starting about four inches out from the trunk spread it out to the edges of the branches - the drip line. Then cover with mulch.

Camellias can cope with sun scorch if they have moist but not soggy soil. They just look a bit ratty, yellow and miserable.

Possibility: if your soil is naturally alkaline then the Camellia may be having trouble picking up trace elements it needs. You may need to get a particular sort of fertiliser to help the plant cope.

If you can see Rhododendrons, Camellias and azaleas all thriving in your area then alkaline soil will not be the problem, unless someone planted it over a pile of mortar rubble. Try feeding first using the compost and clippings, followed with reliable summer water.

PS - if you need to prune it back do so directly after flowering as it develops next year's flower buds over the summer. It will come back from older wood, too.

About the mulch and strips - unless you have fearsome winds I 'm thinking you'll have more trouble with foraging birds shifting your mulch and strips won't help at all! You might consider using a heavier grade of mulch. If your slope pitch is abrupt then a green groundcover may be a better option for soil protection.

Plastic edging strips are a pain...they get caught in the mower and you have to use the weed eater to keep them neat.
Spade edging is easier and brick sunk to mower level is the best!
damp down the mulch when you first apply it, it will soon hang together and not blow away.
I live in Iowa.....and believe me I know wind!
Linda C