Rabbits molt four times a year; December-ish is when they commonly have their winter molt. Molting differs from shedding in that the rabbit loses and replaces their ENTIRE coat in a short span of time. Molts can cause a rabbit to look very odd - you often see a significant "molt line" (or three, lol) at the points where new coat meets old coat, it's possible for actual bald spots to occur during a molt and some rabbits have even been known to experience a very noticeable change in fur color or markings/patterns during a molt. Some molts "migrate" - they start at one (or more) points on the rabbit and systematically progress up or down their body; other molts are extremely arbitrary/random (ie hair coming out all over the place with no apparent pattern). Some molts are pretty explosive while others happen more slowly. Also, molting can be a bit taxing on a rabbit's body, which could explain her reduced activity.
That poop doesn't appear outside the "normal" range to me (ie doesn't look indicative of a specific health issue) - my Holland's poop has always been a little smaller and darker than my Lionhead's and looks pretty similar to the poop in your picture. However, I don't know what her poop normally looks like (for comparison purposes), so I can't determine if there's been a significant change.
The biggest health concern with a molt is the potential for hairballs, since rabbits are physically incapable of barfing them up like cats do. The best prevention for this is to brush or comb your rabbit at LEAST once a day during a molt, removing as much of the dead fur as possible. My tool of choice for this is a furminator (cat, small animal or small dog versions will all work), which is stupidly expensive in most stores but can often be found for $20-25 on Amazon or eBay. I swear by the furminator (which comes with a money-back satisfaction guarantee, by the way) as the fastest/most efficient way to groom a molting bunny, but if you'd rather not cough up for one then a simple dog or cat brush or comb can still get the job done (just make sure it doesn't have wire-tipped bristles).
If a rabbit gets a hairball that they're having trouble passing, it can lead to GI stasis... suddenly not eating and/or pooping (or a sudden decrease in either) is a sign that there's a problem. If a rabbit goes 8-12+ hours without eating and/or pooping, it's a medical emergency and a vet visit needs to happen immediately.
As long as your rabbit isn't showing any symptoms or odd behavior beyond being a little less active and losing a lot of fur, then I really doubt there's anything wrong with her and I think she's simply going through a molt.
That said, a vet visit is NEVER a bad idea and I always urge people to trust their "mommy/daddy" instincts - if I (or anyone else) tell you that your rabbit sounds normal/healthy but your gut is telling you to take her to the vet, then you should absolutely make an appointment to take her in.
There's a reason I **** near never tell someone "you don't need to take your rabbit to a vet" with absolution, particularly when that person already feels the urge to do so. Maybe you're being paranoid... but maybe you're subconsciously picking up on something subtle that you can't put your finger on or relay to us - either way, a vet visit will ensure that your rabbit's health is being properly tended to (and hopefully alleviate your worries).
Back to the topic of poop...
this site does a wonderful job of explaining what your bunny's poop is trying to tell you.