It'd be interesting to know if she wants arty and / or autofocus, and also different ranges.
If she wants to photo anything / everything l am guessing that includes distant scenery > 100 metres away? In that case manual focus lens + adapter might not be viable, as she'd lose infinity focus.
Would it be possible to buy a menagerie of adapted manual lenses + a native autofocus lens?
The following Canon EOS adapters will open up a galaxy of cheap manual lenses you can use, and you might still get far focus if the lens has a very long focal length (these adapters tend to be quite slimline at least for the EOS)?
P/K
M42
M39
P/B
The adapters are very cheap (as low as £5). The lenses can be had for as little as £12. Don't be put off by adverts stating "a small patch of fungus". You could get a bargain with such lenses, the fungus wouldn't have any visible effect.
People consider arty to be f/2.8 or lower numbers, but you can get arty shots with anything. (ok ok this is really blase, sorry)
Then, one of the autofocus lenses people have mentioned for your Canon EF / EF-S mount camera.
If she doesn't do the dishes confiscate it all and replace it with an M39 mount enlarger lens and an M39 to EOS adapter.
Total cost: as little as £120 for 3 adapters, 3 manual focus lenses plus 1 native longer focal length autofocus lens for your Canon 500D. Possibly even lower if the adverts mention inconsequential fungus spots. Oh and a few quid for the rotten M39 enlarger lens hehe.
Welcome.