The email cannot change for work reasons and she uses outlook as it is the only thing that works for her work meetings ( apparently ) anybody using gmail etc had large issues
Most people with internet accounts don't use 3rd party email. To do so, you have to log on to their website. Instead they use the email from their ISP.
You have chosen to do neither. So it doesn't work.
That error is most likely caused by the new ISP blocking standard SMTP ports to all but their own servers as spam prevention. You'll have to find out from TalkTalk if they support alternate ports.
I switched my parents from TalkTalk ages ago since they were a nightmare to deal with! I've signed them up to 1&1 webmail and life has been much easier. No more calls from them asking to "fix the email". I've been very impressed with the service and I'm going to sign up myself once my current contract runs out.