Lisa. I don't have M. Koenigii, but I do have M. Paniculata.
Murraya's are related to Citrus, in the Rutaceae family.

Since the trunk is green, your plant is alive, so don't toss it.

A south or west window is best.
If you can add artificial light, it'll help.

Soil should be well-draining, and a little on the acidic side.

Let soil dry in winter...it should look crumbly, not to the point it cracks. Especially since your house gets so cold..
How do you sleep? I'd be freezing. lol.
50F is chilly, but it won't kill your tree..the lower the temps, there's more chance of leaf drop. That's another reason it's important soil doesn't stay constantly wet.

No need to fertilize during winter. Once your plant sends out new growth, give half-strength dossage. Mine gets Citrus Fertilizer. If you can't locate a Citrus type, a balanced fertilizer like 10-10-10, etc, is sufficient.

During the day, spray leaves, and if possible, shower in sink or tub, once a week.

How tall is your plant/tree?
They're neither slow nor fast growers. With a little work, you'll have a lovely plant..Flowers are extremely fragrant, and can flower throughout the year. But they're mostly summer bloomers.

Here's a pic of my Murraya..It was purchased 1999 at Osco, lol.

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If possible, set your Murraya outdoors in summer. Good luck, and don't give up. Toni

I have two small trees of Curry leaf tree in ground. We had 2 months with night temperatures below 50 F, the plants became dormant, shed their leaves but sprouted back very nicely now and are blooming as well. I think yours will be showing some life in near future.

Izhar