Until you get her to understand the concept of "Safe computing Practice" you're wasting your time it will be a vicious cycle of infection, no matter what you install. Malwarebytes Pro would be a waste of money.

Prevention should be first and that starts with safe browsing habits. Her identity and financial security could be at risk too if she uses the computer for banking, or purchasing on line.

If she is infected now the user should see a Malware Removal forum we could guide you there. Most forums will not tolerate repeat requests if the user can't use the computer in some sort of responsible manner.

Maybe give her microsofts free security essentials
it turns your things red when you do something wrong
certainly gets your attention fast.

I agree with Mikie on the free and fully automatic Microsoft Security Essentials program. You should recommend that then tell the friend if she gets infected again afterwards you will block all incoming emails from her to protect yourself.

Sadly other people do come into the equation when security is being considered. A sloppy contact can cause misery for all those they have on their contact lists.

Stop helping your friend fix her computer. Let her start paying for professional help and I bet her habits change quickly.

I try to educate those kind of people because until they are educated on how to be safe and what practices to use there really is no solution. So I would try leading them to informative sites with good tips and helpful info on things they can do to learn how to be safe and how to help prevent infection. Plus I always install the following programs on their pc as well as making sure they have an updated working antivirus program. Malwarebytes free, superantispyware free, spywareblaster free (has to be opened and updated weekly then enable all protection no scans so very simple) those at a minimum should be on the pc.

some links that can be informative
Learn Safety
Using the Internet Safely
Using the Internet Safely

It might sound strange but for some people the best ones are the ones written for children they can be easier to understand.
Safety on the Internet

I personally learned a ton by participating on help forums and still do today.
But you can only do so much for a person the person has to want to do it for themselves!

Thank you all for your help.
She does want to do the right thing, but my friend is intellectually challenged.
Raven, thank you for your kind insight. I hope that your links will help her understand.

but my friend is intellectually challenged

Ah, a different situation then. You might consider installing the Microsoft Security Essentials program as I noted above. This is because it is fully automatic and relieves your friend of the worry/stress of having to update or run a program.