I think my friend's a hypocondriac, how can I help her and to help her deal with this?

I have known my friend for 20 years. We're both 31, so were obviously 11 when we met (at the beginning of Secondary School), within the U.K.
She's one of my best mates, we've been through a lot together.
Around the time she had her first child, at the age of 18. I first noticed a change in the way she was behaving. She was diagnosed with post-natal depression when her first child (her son) was born. He was having 'epileptic fits' at the age of 6 months old. I used to help care for him when he was a baby whilst she went to work. These 'fits' turned out to be something a lot more sinister, he was diagnosed with a brain tumour. He had an operation to remove 3/4 of it but the surgeons couldn't remove the whole lot due to the fact it was the size of a golf ball and also it would've possibly killed him.

He's now 12 and at secondary school, doing well but has special needs due to needing extra help because of the tumour that still remains in his brain. He goes to a special school for extra help.
My friend now has 4 children in total, ranging from the ages of 12 to 2 years old. She also has a step-son. I don't need to go into mass detail but she left her previous partner and met another man and had 2 children with him. 2 with the previous, 2 with the present partner and 1 stepson which's his from a previous relationship.

She has suffered with anxiety and panic attacks over the years and has been on prozac and god knows what medication. In fact, some of these actually made her really loopy!
I work with children with special needs myself and I have studied in mental health, I have seen her through some really bad, ropey times. It hasn't been easy and i've stuck by her side all the way. I could've walked away like many of her friends did when they found out she was pregnant.

Since the diagnosis of her eldest with the brain tumour (who's being steadily monitored over the years), she has turned into a real worrier of herself. Every sneeze, cough, hiccup, burp, headache etc. She thinks she has this type of flu or that type of flu or this illness or disease, etc.

I used to give her lots of reassurance and then realised what was going on because it was constant illness after 'illness'. I know we all get ill from time to time but this felt like it was taking the mick.

I stopped giving her the attention and then I noticed she tried it from different angles to seek it. If it wasn't an itch, it was an ache and so on and so forth.
She has cancelled meeting up on several occasions. I now know this is down to a confidence thing and perhaps anxiety. I studied a bit of psychology, so I know a bit about how the mind works. I'm no expert though.
Just last weekend she asked me to come out to help choose wedding dresses (she's getting married next June). I feel overjoyed she's asked me to be bridesmaid, i'm totally honoured. Then a few hours before, she text me saying she felt awful and had conjunctivis, the flu, ulcers and then a sorry, I can't make it. I was actually expecting this! I knew she would text me to cancel. This is how well I know her. I wouldn't relent to this though and I told her i'd bring flu stuff that would help her symptoms and something for her ulcers, then I joked I won't come near your eyes, so don't worry.
She came to meet me and I offered her the flu medicine to which she declined and then said it was a dust allergy, as for her eyes it was hayfever and the ulcers had (miraculously) disappeared!

I'm a great believer in ignoring people who seek attention but this has gone on for so long now, I feel she needs help but I don't know how to go about it without offending her. I seriously think she has a problem with all these illnesses she keeps thinking up, if it's not one it's another. I know I was wrong to give her the sympathy she needed before but I honestly didn't know this kind of thing existed properly. I have stopped asking her 'how are you?' now, because I know i'll be greeted with a whole list of 'I have this, that symptoms' and even though I don't ask how she is, she will still continue to tell me that she's been sneezing and is contagious. In fact, i've never known her to be 'well'.

I know this is long and I could probably write a book on it but this is the short and long of it. Thanks for taking the time to read.