Hi Vicki - Thinking about you and your daughter. Stay strong, music is certainly something that can help such a lot.
Right, amp vst's in Reaper......
Firstly download an amp vst - A decent free one to download is Freeamp - The link is here
http://www.vst4free.com/free_vst.php?plugin=Free_Amp_3&id=580You will need to unzip the file and extract the .dll file - Then place the dll file in your Reaper VST folder, this is under Options > Preferences > Plugins > VST (VST Plugin Path)
Now the decision as to record "dry" or "wet" - Everybody has their own preferences but personally I record dry (No FX) as then I can apply any FX to what I have recorded and if I don't like it I can try another one.
So - Record some guitar.....
Once you've done that, click the FX box and choose VST:FA3 Full Fretted Synth
On the top dropdown are various presets which you can apply to your recording - I like to flick through them to hear the different sounds
If you just want tremolo, on the box at the bottom that says "bypass", click the right arrow until tremolo appears - You can then change the rate, depth and waveform. You can apply more FX to the tremolo by using the other boxes at the bottom of the screen.
There are lots of amp controls and speaker settings as well which you can play with. The possibilities are pretty endless
Hope you manage to get that sorted Vicki - Any problems please let me know.
All the very best to you and your daughter
John