There's many problems that can cause leaf drop but most can be put at the feet of your watering.
Combine all the other reasons and they still cant come up with the number of problems due to watering. That includes under-watering; letting the soil dry out too much, then watering to excess.
Too high a temperature at night; in a location too near a door where cold drafts hit it; or placed where heat from the furnace air hits it; or water that's too cold...like straight out of the tap; (let water sit overnight); water that comes from a softening system.
The one that could cause such a problem when all the other reasons have been tossed out; changing the size of the pot from one to a much larger ...i.e. from say a 6" or 8" to one of 12". The roots are then forced to go out further for nutrition--much to the chagrin of the roots which likes it more compact.
Sometimese when a plant is forced to grow--such as repotting, the sun's low intensity cant support the new growth and the first leaves to feel it is the lower ones.
If the lower leaves are seen dropping, its usually due to low light. Change location to offer more light. To do that you might try putting the plant higher--as on a pedestal or table, or hanging up, or on a shelf. A room with walls painted a light color can often reflect light that otherwise wouldn't be there.
Generally, unless its necessary, repotting should be done when the plant is wanted to grow--as in spring. The sun can then support the growth.
Fertilizing a plant when it cant use it...if its not growing then no fertilizer should be given....albeit feed a much lower rate.
When fertilizing, water the plant first, then mix the liquid fertilizer. The water first given aids the fertilizer going to the roots.

I think that it's an over-simplification to put most issues causing leaf drop at the feet of watering habits. That's like saying that the cause of most traffic accidents lies at the feet of the driver's use of brakes. It can always be argued that if the driver had only used the brakes earlier, there wouldn't have been an accident; but upon closer examination we often see the contention set aside in favor of a reason that goes deeper and has more qualifications attached. I'm quite certain this issue goes deeper than just watering habits.

There is no credible evidence I've seen, and I've chased the issue a considerable distance, that watering with cold water causes leaf loss; and while sudden cold drafts can cause leaf loss, this plant doesn't have the look of the problem having been caused by light issues, cold drafts, warm night temperatures, or the plant being too close to a heat source.

The most usual causes of older or lower leaf loss are several. Natural senescence (aging), a N deficiency, tight roots, and low light, are the most common, and deserve equal consideration as the primary cause.

There is a difference between repotting and potting up. While potting up can be undertaken at any time with little in the way of ill effects, as long as you are careful about over-watering until roots have colonized the entire soil mass, repotting is BEST undertaken in the summer months - in most cases between Father's Day and July 4th would be considered ideal.

No plant likes it's roots 'compact' or congested. The grower may at times use the stress associated with tight roots to bend the plant to the grower's will in any of several ways, but its a surety that the organism as a whole will not appreciate the stress associated with root congestion.

Al

cunningleah, "Last winter/spring, it began to drop leaves. I moved it to a new pot, fed it, and moved locations." Can you imagine what that means to a Ficus?
The present location has a lot less light and if you kept the same watering routine, it is very likely that the previous stresses have been intensified.
You can probe the soil in the container to determine the moisture status. If it is too moist then try to dry it out by increasing air circulation at the soil level (fan at floor level?). Admit some more light to the area (open Venetian blind?) and, of course, hold off on the water.
The brown leaf at the top left, the browning leaves on the upper right; and the folding in half, backward along the midrib, as shown by the leaf in the lower fore ground - are all symptoms that you do not want to see on a plant that you do not want to lose.
The encouraging aspect is that the rubber plant is one of the most resilient plants I know. The chances are good that you will be able to save it. I once had to get rid of a large specimen outdoors. I had to resort to a slow fire at the roots to achieve that.

Thanks for all of your advice! I have moved the plant back to the sunny spot of the house and will be more cognizant of my watering/feeding habits. I hope I can get it to live until springtime. Winter in Minnesota is often sunless and cold. Thanks again, Leah

Thanks for all of your advice! I have moved the plant back to the sunny spot of the house and will be more cognizant of my watering/feeding habits. I hope I can get it to live until springtime. Winter in Minnesota is often sunless and cold. Thanks again, Leah