If you were near me that is exactly what I would look for. I'm 5ft5 ish and wouldn't be put off by the size. I would be attracted to the £10 a day/ride statement. When its worded as £30 a week - it gives me the cold sweats! would you be happy for someone coming just once a week though?
I had lots of replies to my adverts (apart from the 13.2hh who needs a very confident rider) with something very similar to the following advert used on preloved and in the local tack shop.
However I think your mares size would put a lot of people off.
Competant sharer required for 17'2 Irish mare.
... is a well mannered, safe hack who enjoys both jumping and schooling. Days and chores negotiable, contribution towards costs required.
We are located in Cowfold, West Sussex on a friendly yard with excellent facilities and access to miles of off road hacking.
Please ring for further details.