Iím a new orchid grower and want to save this orchid!

Iíve had her for about three weeks. Lovely full blooms, but lately the older blooms have started to wilt. There is also a yellow leaf under the big green leaves.

She is in an office with low light and it does get a bit chilly, but the roots look bright green and happy. I mist frequently. What should I do to keep her healthy? Should I cut the blooms? Will they perk back up?
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