But ask her to scribble a message on a post-it note, or sign her name on a form, and she quails. Her handwriting is her biggest handicap.
At its worst it can be like a sickly ant trail, minute and cramped with badly formed letters joined in all the wrong places. Her friends laugh at her holiday postcards; they can't read a word of her crabby writing.
Although she uses a word-processor whenever possible, there are still some situations where she is forced to pick up a pen: "It can be embarrassing when I have to leave a note for someone," she says, "and if I have to take notes in a meeting, then it's quite a labour. I have to read them back and type them up immediately, or I'd lose them."
Like many otherwise well-educated adults, Marion is embarrassed and frustrated by her poor handwriting.
Dr Jean Alston, honorary president of the Handwriting Interest Group, which was set up to promote the teaching of good handwriting in schools, says she gets several calls a week from desperate adults whose handwriting is a hindrance to the normal running of their lives. Indeed, very occasionally it can ruin a career.
Earlier this year, an anaesthetist was criticised by the Westminster coroner for his unclear handwriting, after a patient died following what should have been a routine operation at a private hospital. A colleague had misread the squiggled dose on the prescription as 30mg rather than 3mg of the painkiller, diamorphine - with fatal consequences.
Alston believes it is nonsensical that handwriting problems are so prevalent among adults, "when there are only 26 letters and three joins to master".
She puts this widespread failing down to several factors: the greater use of word-processors, which means people write less by hand; the use of modern pens, such as rollerballs, which need to be held upright and encourage the wrong kind of grip; and, most significant of all, a laissez-faire attitude to teaching handwriting in many schools.
She explains: "Some schools have concentrated on print script rather than joined-up writing. Others have let children write for several years before teaching them to form letters.
"The national curriculum in the early days stressed handwriting. Now, although it still says children should be taught to form letters, handwriting's not got such a prominent position, it doesn't attract so many marks.
"Although many primary teachers have bought a scheme, many still don't understand how to teach the subject. They think if the children copy the work cards, the handwriting will take care of itself, but in fact the children may be copying, using the wrong movements."
Alston believes there's a need for handwriting courses for adults, but there is very little on offer. Many adult education centres offer calligraphy or graphology, but nothing for developing a fast, plain script. Adult literacy schemes are pitched at those who can't read or write at all, rather than the professional who scrawls.
Marion Hilbourne believes her writing deteriorated when she changed school at the age of ten and was made to change from a loopy style to a non-loopy one.
But she hasn't given up. A few months ago she answered a magazine advertisement for a handwriting correspondence course. Now, two-thirds of the way through it, she can see improvement. "The letters are better formed and I can read the writing more easily," she says. "It looks quite childish and unformed, but with practice I hope it will develop into a more mature hand. "
The course she signed up for is run by William Batten, a retired primary school headmaster, who claims it is the only one of its kind in the country.
Batten has always taken a pride in his neat writing and discovered during his career that he had a talent for diagnosing handwriting problems.
He was inspired to start his course last year when he took on pupils as a private tutor, and found the parents were envious of their children's improved handwriting.
Batten's scheme is based on the principle of developing a clear model script, and then practising to build up speed.
"The key factor is maximising the pen-to-paper contact, so you haven't got to stop at every letter and start again," he says.
He offers two styles: the round (down strokes, like a monkey's tail) and the cursive (more loops - a development of old copperplate handwriting). Students send a sample of their handwriting when they apply, so he can diagnose any obvious problems.
They start off learning to form individual letters, then progress to joining pairs of letters, three-letter words, common double-letter joins, and capitals. There are 50 carefully graded assignments, and at various stages students send their work to be assessed.
In theory the course could be completed in seven weeks, although students can take as long as they like. Fifteen minutes of regular practice each day is more productive than an occasional hour, Batten says.
Most of the adults who come to him are only able to print or semi-print, and find writing laborious and slow. "Nine times out of 10 it is possible to improve people's handwriting, provided they're committed and practise the exercises," he says. So far, he hasn't had a student who hasn't improved. His oldest pupil, a man of 68, promptly enrolled his two middle-aged sons when he finished the course.
* William Batten, Centigon Education Services, 7 Carlton Close, Racecourse Lane, Shrewsbury SY3 5JA. Tel: 01743 243185. Correspondence course costs Pounds 85 (five modules) or Pounds 18 for each module. Teach-yourself course costs Pounds 35. One-day intensive course on an individual basis costs Pounds 95. Handwriting Interest Group, Felicitie Barnes, 6 Fyfield Road, Ongar, Essex CM5 0AH