Coumadin/Warfarin (brand and generic names of same drug) is a medication that requires regular bloodwork to be sure it remains in the therapeutic dosage. You did not mention this, but I'm assuming your mother goes to "Coumadin clinics" for these check-ups with a nurse regularly, right? If not, please check into that. You did not mention if her physician is a cardiologist, internist, or what. When I was a cardiovascular pharmaceutical rep a few years back, the Coumadin Clinics were primarily at cardiology offices, as I recall.
You didn't mention your mother's age or how she feels about her Dr, but I encourage you to be sure she is seeing someone she and you feel listens appropriately to her concerns & yours. Just as in every other profession, there are more and less attentive physicians out there and, sadly, there are still some who "pooh pooh" as you put it women's concerns about their health. Find one who doesn't. Of course, insurance coverage and where your mother lives will play a role in who she is most readily able to see.
Side effects can be related to one medication or a combination of medications taken or even a combination of medications taken and when and how they are taken! Some medicines need to not be taken with others or with certain foods (grapefruit is frequently a problem with some cardiovascular medications, for example). Please be sure your mother and you are aware of any such restrictions for her. Having said that, I caution you not to become overly alarmed when reading the information that comes with medication at the pharmacy!
The American Heart Association (another previous employer of mine!) has a great website that might provide some more answers and resources for you. Pharmacists, nurses (not so much MAs, but LPNs, RNs), as well as your mother's Dr/PA/NP should be considered resources for these questions.
Also, I hope your mother will not rule out the possibility that life changes such as that recent death COULD be playing a part in what she is experiencing. I'm guessing this isn't the first family death she has ever grieved, however, so I imagine she'd know if what she is feeling is attributable to that or not. Depression is a real illness and should be treated as such just as cardiovascular illnesses are.
Sorry for rambling on so long. I hope some of this was helpful.