Jailbroken Phone playing up

[PurplePaws]

I gave my mum a jailbroken 3GS, it was already jailbroken when I purchased it, and I haven't been able to find the person we brought it off to help with the issues we are now having.
I have once plugged it into my pc and restored it, which came up with an error and wouldn't restore and was not usable. I managed to find the person who sold to me, and he fixed it within 15 minutes!
I suggested to my mum to use the phone as a hotspot through her laptop so she could use the internet. Ever since she has done that, it now shuts itself off and restarts.
I have no idea about jailbreak, but I do know it has Cydia and Winterboard. In your honest opinion, do you think it is something I can fix easily, or best for me to find someone to pay to do it?
As my mum lives 2 hours away from me, she will need to be without the phone if I take it away to get it fixed so I am exploring all my other options before I do take it away from her.
I have read a lot of posts on here and I notice that there are only a select few who reply to these, so I really appreciate any advice that can be given whenever it is suitable