From you you have put here, there should be no foreseeable problems with passing your pc on. However, it would be an idea to ensure that your e-mail account and internet log-on is no longer on the machine. In addition to this, and not knowing the nature of her disabilities, it may be worth seeing if there are any accessability options that could be of help. These can be found in Control Panel - Accessability Options.
In terms of upgrading from CRT to TFT, this could be considered a bit of a luxury if the CRT is working well. If so, your only real gain will be space-saving. (19 inch CRT's can also be a bit of a hand-full when moving it around!)