OP wrote:
" 4 GB of memory, and 500 GB SATA Disk HD. She only uses it for surfing the net, email, writing papers, etc...If I were going to do only one upgrade, what would you recommend? Funds are tight."
OK, you need 3 cheap things:
1. ONE 8gb RAM DIMM. Replace the topmost DIMM (when the back plate is off). This will give her 10gb of installed RAM, probably all she'll ever need.
Hmmm... see you already added RAM.
BUT... that's not going to be enough.
You need a faster drive, So... keep going...
2. A 500gb 2.5" SATA "bare" SSD. Buy "for price", not speed. Then get...
3. An enclosure for the SSD:
SABRENT 2.5 Inch SATA to USB 3.0 Tool Free External Hard Drive Enclosure [Optimized for SSD, Support UASP SATA III] Black (EC-UASP)
tinyurl.com
This stuff won't cost very much.
Then do this:
a. Put the SSD into the enclosure, plug it into the Mini.
b. Erase/format the SSD to "Mac OS extended with journaling enabled, GUID partition format".
c. Download CarbonCopyCloner from here:
www.bombich.com
CCC is FREE to download and use for 30 days -- costs you nothing to do this.
d. Use CCC to "clone" the contents of the internal drive to the SSD.
e. Go to the startup disk pref pane and set the SSD to be the new boot drive.
f. Reboot. Do you get a good boot from the SSD?
If so, all done!