Mobile User unable to log into our web site

We have a new mobile product in beta test with about 50 or 60 Users.  This is our first foray into mobile software so we are learning as we are going.
The User logs on via the browser on their phone or PC, but most use their phone.
One User (and only one User) has complained that she cannot log on.
She enters her e-mail and password correctly, but when she selects Submit to log on her page simply refreshes and presents her with a new blank log on page (no error codes indicating incorrect password/email entry or anything else).
We have confirmed that her account and log on details are correct and have successfully logged on as her on several different devices.
It is obviously an issue with her phone (Apple iPhone 5 / Safari browser) but we are at a loss as to what advice to give her.  We are setting up a log file so that we can at least check if she is connecting with us.
Any ideas as to how we might help her would be most welcome, and what we might do to prevent this in the future.
Who is Participating?

[Product update] Infrastructure Analysis Tool is now available with Business Accounts.Learn More

I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

Gerwin Jansen, EE MVETopic Advisor Commented:
What kind of phones/browsers do the other users have?
Are there any users that have Apple devices as well that do work?
Did that one user try with a different browser, like Chrome?
Chris_RyanAuthor Commented:
Hi Gerwin

What kind of phones/browsers do the other users have?  A variety of phones and browsers, mostly Apple/Safari based
Are there any users that have Apple devices as well that do work?
Did that one user try with a different browser, like Chrome?
She was reluctant to download another browser since this was her personal phone.   We asked her to try Private mode, and this appeared to work for her.

... but we still have no idea what the original fault mode might have been.  So any ideas would be most helpful
Gerwin Jansen, EE MVETopic Advisor Commented:
Assuming that the private phone is up to date with latest IOS and similar devices work fine, I'd be interested in what your logs would say. Some setting in safari probably, since private mode is working (this would also mean Chrome would be working as well). So not a Safari general issue. User isn't part of the Apple Beta software program right? You could check Safari versions.

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today
Responsive Web

From novice to tech pro — start learning today.