All right, it has been several days now, and I have not gotten any more blue screens, so I think that the issue is probably resolved.
I not only posted on this tech forum, but I also posted on several others. I received different advice from different forums, and I'm not sure which thing actually resolved the issue, but I believe it is only fair to include the solutions that were offered on other sites, too -- just in case someone else has a similar issue.
Here is a summary of everything that I was asked to do:
1. I was asked to find the minidumps and zip them together and post them on one of the forums
2. I was asked to remove the broadcom device and its driver, and then reinstall it
3. I also was asked to check to make sure other drivers were up to date
4. I was asked to install a hotfix from Microsoft
https://support.microsoft.com/en-us/kb/2528614
5. I was asked to test the hard drive using Seagate Seatools (both tests passed)
6. I was asked to run Memtest86+ for three passes, and there were no errors
Things I've done on my own:
1. I ran CHKDSK
2. I had Sophos, which is my friend's antivirus, scan the computer for viruses. It found and fixed one problem, and then gave me a list of 11 spyware/adware programs that I had it clean from her computer.
3. I ran disk defragmenter
4. I updated her Firefox and Google browsers, and I had it update her extensions on Firefox
5. There were some Windows updates that said they were ready to install yesterday, so I installed those
If the issue comes back, I will let you know. Otherwise, consider it resolved.