Think you have made the 'hardest' move, by putting the ad up and being
totally honest about your experience, good for you.
Make sure first of all you see this Horse ridden by an experienced rider/Owner
before you get on, also see this Horse hacked out in traffic etc., so that you know it is relatively safe, if thats what you are planning to do, but bear in mind that no matter how well behaved there is always the chance that something can give a horse a 'fright' unexpectedly when you are out and about, but you can see its behaviour and get a general 'feel' of temperament etc. by watching it be ridden. Its VERY important that you don't just 'jump in' and that the Horse IS suitable for someone with your level of experience. There is nothing worse than being 'overhorsed' (most of us have been there) but it WILL dent your confidence, so no matter how tempted you are, hold out for the right Horse for your level of experience.
Ask a bit about Horses general health and if there is anything in particular you should know about, i.e. back problems, arthritis, laminitis. How often is it shod or is it barefoot. What costs would be involved, if any

)) and what would be expected of you. To be fair, you have been honest and I would
expect you to receive a fair bit of help/guidance initially anyway. Ask about ANYTHING you have even
the slightest doubt about and IF it comes to drawing up a Contract make sure anything you have any
worries about is covered, in fact, cover every eventuality in the contract.
Ask if she wants a 'full loan' or part loan/share and if she would be prepared to
draw up a contract (ALWAYS ADVISABLE, CAN SAVE LOTS OF HEARTACHE
DOWN THE LINE).
Basically you need to find out if this Horse is suitable for your level of experience, that the Horse is relatively healthy for its age with no underlying problems, especially IF you are going to be contributing to vets bills etc., (ask about Insurance and if the horse is covered). What other contributions
you will be expected to make, how often you are allowed/expected to ride.
Hope it all works out for you, bear in mind sometimes loans/part loans etc., are very successful, sometimes unfortunately they don't work out for differing reasons. However, when successful they are a fantasic way to enjoy and experience Horse ownership.
Sincerely hoping yours is successful and that it all works out and you have lots of fun.
PS. for anyone looking at my times of posting tonight, lol, I AM WORKING a Night Shift but we are
QUIET.....so cannot resist 'looking in'