Well it is from first hand experience.
To give an example.
I am considered bipolar type II. Which is the most common but rarely diagnosed because no one seems to notice and very few are diagnosed with type II. Type II are generally called “eccentric” people.
Type II is Mania with small episodes of depression on the average. So in other words I am happier than normal 90% of the time. Mania is like being on the best drugs in the whole world without ever coming down. Grandiose ideas, feeling unstoppable, or bullet proof. Since no one really goes to the doctor because they are just to damn happy all the time very few people are diagnosed with type II. 
Type one is like this. Say “Normal” is 50%. Say the happiest you could ever be in your life is 100% (Mania) . Now picture losing every loved one you have ever had in your life in a plane crash. That is 0% (depression.)
A manic depressive (type I) individual would be around 0-10% most days out of the year with small episodes (from maybe a day to two weeks) where they would swing to about 70% (sometimes 90 or more but rare) and fluctuate a little before settling back down to around 10%.
A Mania (type II) sits around 90% most days and then swing down to about 30% a few times.
This is cycling. Now if they are a fast cycler they could go from 20-90 and back again in a very short time. THese are the individuals that it is most noticable that they are mentally ill because their moods switch so fast. (Fast Cycling)
“Manic Depression” is actually Bipolar Type I where one is depressed most of the time with some Manic episodes (Happier than normal).
Now take my wife. She is “Manic Depressive” (Type I) where I am Manic (type II).
Or a layman term pessimist (type I) optimist (type II)
Now about the medical conditions they are true. Believe me. I have taken my wife to the doctors plenty of times for anxiety, IBS, stomach nausea, ulcers, etc. And plenty of Doctors have explained that this is common in people who suffer depression. They literally make themselves sick with worry. Also studies have shown relations between Type I, Type II and compulsive disorders.
The big differences are this and I will put this in a very general layman analogy if I can.
A mania or hypomania episode is like being on cocaine, PCP, and Ecstasy without any narcotic effects. You feel alive, on top of the world. Like you just conquered the world. Sounds great but it is damaging because you do NOT rationalize the cause and effects as normal. You are overly optimistic. You talk fast, sleep little, have very little appetite, start many projects but never follow through. In fact many people misdiagnose Bipolar Type II as ADD or ADHD. When you cycle down you tend to get angry, irritable, and irrational with some depression. Like going through withdraw.
When you fall into depression it is the polar opposite (hence bipolar). You are very depressed, you eat more, you feel tired and lethargic all the time, you worry, you stress, you sleep too much, your stomach acids flow due to the worry causing the digestive side effects I discussed. Also many who are very depressed are worse on dreary days. If it is cold and rainy and my wife is on the downside she won’t even go outside because it is MORE depressing. Depressed people have to motivate themselves just to climb out of bed. It is very difficult dealing with depression and this can lead to poor diet, weight loss or weight gain, hi-blood pressure, digestive problems, etc. Imagine being under extreme stress for a long time without any reprieve. Your body suffers. Also you need to take into account the side effects of the medicine if the person is medicated.
Think of a time when you heart was really broken and it brought you so far down you didn’t care about yourself. Now multiply that by 100 and throw in a few deaths in the family. That is a manic depressed person unmedicated on a GOOD day.
On my scale of 0-100. Normal people when they lose a loved one and are really depressed the hit rock bottom at about 30%. Normal people when they have the happiest day of their life they hit about 70%.
So taken into account an unmedicated person suffering depression or mania is either higher than normal or lower than normal. If they fluctuate then they are bipolar either type I (Manic Depressive) or Type II (Mani or Hypomania).
You haven’t offended me
I will tell you that a “manic depressive” is generally viewed as one that is common Bipolar Type I that is is more often depressed than mania where as type II (the more common) is generally more mania than depressed.
As an example in your story snippet.
(1) She sort of sounds Type I and a slow cycler. Ok that could explain why she is overweight or the medicine she is taking to normalize herself has caused the weight gain. Would explain the shame and the feeling of hopelessness about her weight and the anger.
(2) A cold monday morning would be more difficult for a manic depressive than a sunny day. So they wouldn’t rise out of bed. They would more likely force themselves to crawl out of bed after a quick mental discussion on why they have to leave the bed to meet the dreary day. 
(3) When she feels the envy in her stomach when she is looking at the skylight she would probably feels some nasuea and a tightness (Physical effects from a mental emotional feeling) that is exaggerated by her illness.
(4) I could be way off base on everything and wasting your time. I can only speak from experience. Me personally I felt the character had more a normal depression due to low self esteem more so than a “manic depressed” person would act. SHe seemed to suffer more from low self worth than depression. I say this because her depression seems normal where a manic depressed person their depression is a whole lot lower. We are talking The Gallows here emotionally. I just get a different vibe from your character the way things are described. I get more of a low self esteem issue and a low self worth feeling more so than deep depression.
Who knows? I might not be the one to ask. After all I am crazy 