Zoho Chat - group member doesn't get any notifications

Hello, I'm the chat administrator for my library's Research department. We use Zoho Chat to assist our students. We created an administrative account and added all the Research librarians to a group under that account; then they each sign in with their own individual login credentials. We started using Chat this way in July 2012 and it's worked well for the most part. However, recently one of the group members stopped receiving any type of notification - no popup, sound, anything. Also, others who were logged in to chat at the time couldn't see her in their buddy lists. My first (successful) attempt to correct the problem was:

Logged in on my computer using her ID (which worked with no problem)
Deleted her from the group and sent a new invite
Created a shortcut on her computer using Chrome (she had been accessing chat via Zoho's website)
Checked to make sure her settings were set to receive visual and audible notifications

I'm not sure which of these things worked or why, but she was then able to use chat again for a few days. Unfortunately, yesterday the same problem occurred and repeating the above steps hasn't helped.

One thing we both noticed was that after she logs in to Zoho chat, the progress bar at the bottom of the page stays in a loading status, even though the chat page itself appears as if she's fully logged in. Others who are logged in can't see her, she doesn't get any sort of notification of an incoming chat, and she's unable to send a chat.

Here are her computer's technical details:

Windows XP Professional version 5.1 (Build 2600.xpsp_sp3_qft.130503-0418: Service Pack 3)
Internet Explorer 8.0.6001.18702IC
Mozilla Firefox 5.0 rv:1.9.2.28
Google Chrome 28.0.1500.95m

To the best of her recollection, she didn't change any browser or computer settings prior to the first occurrence of the problem. And although her computer's OS and browsers are quite a few versions behind, others in our department have similar machines but are not having any chat login issues.

I hope you can help me correct this problem. Thanks!

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