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... It is always darker and sometimes it seems a bit muddy...
This is most likely affected by three things:
1. A reflective print never appears as bright as a monitor - stating the obvious, just for completeness. I know that your point of comparison is an older HP printer.
2. Your choice of monitor gamma setting can make images appear even brighter.
The 3800 has a moderate tendency to print darker than some other printers (a characteristic that was "fixed" with the 3880, which uses a new ink set).
I would not give up on a fully color managed workflow - calibrated monitor, individual paper profiles, using Photoshop or Lightroom to control color. This is the way for best, most consistent results, once you get it set up properly. Lightroom 4 has an adjustment in the print module for print brightness, which I leave at neutral for the 3880, but can help with brightening prints from the 3800. (I use both those printers.) If you do not have nor wish to use Lightroom, you could make and save a Photoshop curves adjustment layer to brighten images only at the printing stage. IOW, do all your adjustments visually as you have been, then just apply that layer to anything you want to print. You'll have to work out the curve by trial, of course, but start by just pulling up a mid-tone point a bit. This should not only increase the brightness but also give a little contrast which may fix the muddiness you see.
Hope this helps some. Best to your Mom and to you.